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Show Plants and Disease. So closely is the idea of suffering associated as-sociated in our minds with that of disease, that it appears at first sight a mere figure of speech to refer to certain cer-tain disorders in plant life as "diseases." A very little reflection, however, shows that the term is fully justified, and that pain, while a very frequent concomi tant of disease in animals, is not its chief characteristic. In fact, such pain may be regarded as a danger signal, warning the organism to take action against an enemy. And 'jnst because the higher plants do not actively oppose op-pose enemies (since they have, hi th( majority of cafes, no mobile organs) there has been no occasion for a sense of pain to be developed in plants. How, then, do plants react against injury? How do they resist such attacks? It may shed some light upon this question if we briefly consider the corresponding cor-responding inquiry: How do animals react against injury? In this case we find that there are two distinct methods : employed. An illustration will best ex-i ex-i plain this point. If the enemy is sufficiently large to be discernible by the senses, the or-; or-; ganism reacts either by seeking pro-1 pro-1 . tection in flight or under cover, or by warding off the enemy by direct counter : attack. But with invisible foes mi-i mi-i crobes this method fails; the oigan-; oigan-; ism then has recourse to physiological i and chemical weapons of defense. Tne j phagocyte or amoeboid cells of the I blood do their best to devour ti:e in-j in-j vading hosts of microbes. At the saint time antitoxins may be manufacture in the body to counteract the toxins o I poisons produced by the bacteria. Nov, a plant is to all intents and purposes blind, deaf, and devoid of all our liner senses. It must, therefore, rear' i against many enemies plainly visit-; ; us, just as we react toward the invirs ; ble microscopic hosts. The fly ali - j ing on cattle in the pasture is prom.i ly whisked off by a member specially provided pro-vided for this purpose. But an insect alighting on a plant is free to make such attack as its nature prompts, for the plant in all but a lew exceptional cases of insectivorutis species, neither sees nor feels the enemy, nor, even if : it did so, would it be able to ward it oil' by action. It is, therefore, only reasonable to expect that plants may in a large measure meas-ure use chemical means to ward off not only microscopic, but also larger ene mies. VV e should naturally expect that plants devoid as they are of active means of defense, should have developed develop-ed to a rather higher degree than is the case in animals, various passive means of defense. Among such there readily occur to our minds thorns and pncKies, j which indeed are extremely common ' protective devices in plants. But is it not very probable that plant luices also ! may serve to keep o!f insects and other ; enemies? If so, we should expect that 'any degree of malnutrition, any de-' de-' ficiency in soil, any excess of moisture or other untoward circumstances, should immediately expose the plant to the danger of invasion of insects and other pests. And vice versa, we should argue that the most rational method of fight ing such invasion would be, not so much to"at tempt the often extremely difficult task of exterminating the preying species, but rather to strengthen the ' lant so as to enable it to manufacture those juices by means of which it wards off eneinie . Pi usible as these conjectures appear, it mus! be admitted that facts are not wholly in harmony with them. For while in some cases plants are very strikingly more susceptible to insects when the plants are weakened, authorities author-ities tell us that in mo.-t cases the insects in-sects seem to find vigor'. us plants just as susceptible as the weak ones. With fungous and bacteii:.! diseases the greater susceptibility f weak plants is more general, althou'i not universal. The cases in which pia:,'s ar,- suffering from malnutrition, abnormal soil conditions, con-ditions, excessive moisture, or other unfavorable circumstances, are very large, however, and such 'plants are found more susceptible to these diseases. di-seases. Scientific Amene: i. |