Show NOTES ON THE BEAN BERN r I Though the bean is one of the most K i common forms of plant life and an article article arti uti- util l cle de of food very little attention has been paid by those interested in vegetable ble histology to the investigation of its structure On account of the familiarity of everyone with its outward out outward ward appearance its shape size color etc I deem it unnecessary to dwell for any length of time on those features here but shall begin at once to describe it as it appears under the microscope It will be well however to say that the bean is made up of two parts an outer shell the and an inner portion portion portion por por- tion the embryo consisting of two lobes almost equal in size and joined together at one end near the Under a low power objective the peri peri- carp appears to be made up of a perfect network of very minute cells almost round in shape The high power objective objective objective tive reveals the fact that they are re not round but pentagonal cells No douht the typical bean cell is t f circular but owing to pressure pressure from adjoining adt adi ad- ad i t joining ones it has in every observed 1 f case become pentagonal or hexagonal The cells on the surface of tLe the embryo are larger than those described above i I and are less uniform in shape They are i roughly pentagonal and have distinct regular walls They differ also in the fact tact that they contain many granular bodies some of which resemble chlorophyll but are probably probably probably ably a form of protoplasm There are also two or three globules of stored up food in each cell If a thin section from the surface of the embryo be treated with a solution of iodine and alcohol ale the globules mentioned above will become become become be be- come deep-blue deep or purple indicating t 1 that they are starch granules There is also considerable cellulose present It may be easily detected by carefully washing the stained iodine-stained section with water then treating with dilute sulphuric sulphuric sulphuric sul sul- acid and again again with iodine More of the plant tissue will be turned blue Another good method method of testing for cellulose is to treat the specimen with dilute sulphuric acid thereby changing changing changing chang chang- ing the starch into sugar and and the cellulose cellulose cellulose lose into starch Then with a solution of potassium iodide the cellulose may be detected N Near ear the centre of the em embryo the cell walls are thicker and still more regular in shape the cells larger and more nearly filled wi with th food materials Instead Instead Instead In In- stead of there being only two starch granules in each cell there are four Jour or five and these are much larger than the others There is some cellulose here but much less than at the surface The cells are so full of protoplasmic granules that no inter-cellular inter spaces can be seen N Nearly early two months after the the- above notes were taken an examination w was s ti made of a cross section for starch It was found that the granules of starch were much more numerous than before Probably the increase is due to the fact that as winter began and the se seed d became more and more inactive more food was stored up in the form of starch The protoplasm also had b become become be be- come inactive and was was was' very gelatinous in appearance THE BEAN AFTER GERMINA GERMINATION ION The Development ment A number of beans were planted at at atthe the same time and under the same conditions conditions conditions con con- and watched for nine days At r t J the end of each day one was dug up and the advancement carefully noted q f First First day The The bean had undergone very little change The had softened a little and the embryo had ber begun begun be be- r gun to swell c Second day da- da The daThe The embryo had swollen considerably and the peri carp had 1 broken a little at the It had t become somewhat transparent as a ref result re re- f suIt sult doubtless of the absorption of oft t moisture t Third day No No marked change except that the embryo had swollen more and andt t the had opened wider ry r Fourth day The The break in the peri peri- r carp had increased to about third one-third Y the length of the embryo and the radi radi- if cle had begun begun to to push its way through J l the opening Fifth th day The The opening had become y larger and the had grown out about one-fourth one of an inch Rapid development had begun and it appeared that most of the energy was being used fl in causing the to grow Sixth day By By the end of the sixth day remarkable advancement had been made The had broken laterally R with respect to the longest axis of the I bean and the had extended about one and one-half one inches At about one- one J half inch from the em embryo a decided enlargement had been formed in the from which point the root had begun and was growing downward The first node of the stock had been formed by a growth in the opposite direction Fr and the embryo was being carried upward Seventh day There There had been a decided decided decided de de- swelling of the embryo and the had begun to detach itself The root had grown out about two and andr andl r l one-half one inches and the rootlets had formed at the enlargement The stalk now about one-half one of an inch long had increased in diameter Eighth day The The root had not become much longer but had grown laterally and more rootlets had been formed r These were about two-thirds two of an inch in length There was a marked increase of the stalk in size and a further enlargement enlargement enlargement en en- at the beginning of the root The cotyledons had separated a considerable considerable considerable con con- distance and the could be seen at the end of the embryo opposite that from which the had grown Both the and the plum plum- ule began from the same point Ninth dav By By the end of the ninth day the had left the embryo and the cotyledons had opened The I was becoming quite well developed developed de de- j I into the first leaf of the bean beant having grown beyond the cotyledons 1 about one-fourth one of an inch There were some indications of chlorophyll The root had branched in several directions directions directions j and each branch had grown about two and one-half one inches j THE HISTOLOGY The Embryo Soon After Germination I The bean imm immediately after it ha has has- begun to germinate presents an appearance appearance appear appear- J ance but slightly differing from that of its inactive state except that some of ot the starch has been converted into sugar and that there is a slight increase of protoplasmic granules in in the cells The cells are pen pentagonal and hexagonal as before At the end of the second days day's growth an em embryo was was' tested for sugar with Fehlings Fehling's s solution with no results When a test was made on the th third rd day a trace of sugar was obtained This points to the fact that 9 the starch is converted into sugar just justas as fast as the plant can use it The First Node of ot the Stalk Eighth Eighth- day A section cross-section of the first node examined examined ex under the microscope showed 1 j that that part of the stalk is IS made up j of two kinds of tissue The xylem is of iI nearly round hexagonal cells and and forms forms a central portion of about three-eighths three of the diameter and an outer ring of about one-half one the diameter The other tissue or phloem consists of very small round cells and forms a ring of about one one- one eighth the diameter of the stalk situated between the two parts of the xylem There are perceptible imperfectly developed vascular bundles in the phloem Since none could be found on the seventh day it is quite conclusive that the vascular bundles begin on the eighth day in the bean hean The cells of the node have very thin walls and contain contain contain con con- tain a little chlorophyll The chlorophyll chlorophyll chlorophyll chloro chloro- phyll also makes its appearance first on the eighth day The Stalk The stalk consists of tissues made up of two kinds of cells and The latter closely resemble spiral cells cell's and are arranged at an angle with the longest axis of the stalk The central part of xylem tissue mentioned mentioned mentioned men men- in connection with the first node has almost disappeared and there is an intercellular space or tube extending through the stalk The cells have thin walls and contain much chlorophyll The LeaThe Leaf Lea The cells of the leaf have thin walls and are of very irregular shape having been pushed into a great many forms The most prominent feature feature- of the leaf structure is the great number of stomata stomata stomata sto- sto mata or guard cells present These resemble halves of apples in appearance and are arranged at irregular intervals in the cell walls Through the sto stomata ata the excretions of the plant plan tare are ej ejected There is an abundance of chlorophyll or coloring matter in the leaf The Root The cells of the root a are e for the most part small and contain a great amount of protoplasmic material The tip is made up of a single row of large cells arranged end to end the central cylinder cylinder t der and several rows of small cells radiating radiating radiating ra ra- from a spot near the end the growing point Beyond the growing point is a mass of small cells without l order of any arrangement M. M R. R Porter r IN |