222 



PLANTS 



The Movementt of Mature Plants which we have 

 now to describe are due to alterations in the 

 turgidity of the cells. The exciting stimulus of 

 Bonie of these movements is known : it may be 

 contHct, light, temperature ; in other cases it is 

 obscure, as we have found to be the wise with 

 MIMIC of the movement* of growing plants. 



Contact. The leaves of the Sensitive Plant (q.v.) 

 droop when touched or shaken ; the stamens of the 

 BwlnridMMB, when touched, bend down and come 

 in contact with the stigma. The tentacles of 

 Drosera bend over, ami the leaflets of Venus' Fly- 

 trap close, when an insect alights upon them (see 

 INSECTIVOROUS PLANTS). 



Light and Temperature. Many leaves e.g. 

 those of Mimosa and Oxalis move up and down 

 with variations of light and temperature. The 

 sleeping and waking of plants i.e. the folding of 

 many leaves and flowers at dusk and their opening 

 in the morning are familiar examples of the effect 

 of variations in external conditions. 



Spontaneous Moventents of Mature Plants. The 

 leaves of some few plants e.g. the Jln/i/mirinn 

 gurans rotate in the dark, while the leaves of 

 Mimosa, Oxalis, anil Trifolium move up and down. 

 These movements are not seen in daylight, prob- 

 ably l>ecause they are olcured by the movement* 

 due to light. The movements of the leaflets of 

 rtesmottium gymmi are dealt with at TELEGRAPH 

 1'i.AST. The plasmodia of Myxomyeetes creep, 

 Bacteria and Diatoms move in a way not yet 

 understood, Volvox swims by means of cilia, the 

 zoospores of Algne and the antheroids of Mosses 

 and Kerns swim after they have been set free. 



MKIUCINAL PLANTS. The study of plants with 

 genuine or fancied curative properties is as old as 

 human thought and sickness. Even animals seek 

 such medicines, and it must lie remembered that 

 our early ancestors were much more familiarly 

 acquainted with fruits and seeds, roots and bullis 

 than are their more carnivorous descendants. But, 

 while it may be contended that ancient medical 

 treatment was in great part a natural return to 

 more primitive vegetarian diet, it is obvious that 

 men would lie quick to profit by a wide and often 

 costly experience of plants with special properties, 

 poisonous ami emetic, tonic and narcotic, excitant 

 and sudorific. While botanical science is partly 

 rooted in the garden, no small part of it has grown 

 out of a primitive materia medica. Thus, in the 

 writings of Hippocrates (460-377 B.C.) and those to 

 whirh his name is extended 236 medicinal plants 

 are recorded ; the list swells in the works of 

 Aristotle (387-322 U.r.) and Theonhrastus (371- 

 286 H.I-.), while the 'Materia Medica' of Diosco- 

 rides (born in the 1st century A.D.) includes the 

 mimes and partial descriptions of almut six 

 (hundred. His work remained authoritative for 

 fifteen centuries, and WM OODtkuud on the one hand 

 tlnouu'li the herbalist* like Gerard and Cul|>eppcr 

 into the Ixttanical side of the modern pharma- 

 cojMcia, on the other hand through such early 

 iHitanists as (Vsalpiniiis into the independent 

 doubtless too inde|tcm!ent science of Imtany. 



In connection with medicinal plants there are 

 many interesting chapters of history with which 

 the student should make himself acquainted -the 

 weird stories of the old traffic in vegetable poisons ; 

 the magicians' use of narcotics and excitants ; the 

 mystical doctrine of Signatures (q.v.), according to 

 which plant* liorc signs indicative of their virtues : 

 the gradual decay of herb gathering and the loss of 

 much of the ancient traditional lore ; the persistent 

 record of the old uses of plants in lioth technical 

 and popular names, such as 1'iilmonaria, Sanir.ula, 

 Tiiwiilago, and wound wort, scurvy-grans, gout- 

 weed ; the additions to the British Mora by such 

 importations as belladonna; the elimination from 



the modern pharmacopoeia of many vegetable drugs 

 whose value was only fanciful ; 'the relegation of 

 others to the list of spices; the modern discovery 

 or rediscovery of the potencies of Calabar brail, 

 cinchona, coca, and many more. 



See BOTANY, MATERIA MEDICA, I'HABHACOPOUA; 

 Woodvillc, Medical Botany (4 volg. I7!); lUyiie, 

 Sachrnbunv der in Anrntituude ytbraueh/irhen. 

 (/orach* ( 1805-46) ; N von Eaenbeck, Wcihe, Walter, 

 nd Funke, Sammlung drr officineller J'Jtanzen ( 1821-33 ) ; 

 IScntley and Triuien, Medicinal 1'lantt (4 voU. Lend. 

 1877); Luerssen, Aledicinuch-Pharmaceutucke liulanik 

 (Leip. 1877). 



DISEASES OF PLANTS (Phytopathology). Scien- 

 tific investigation of the diseases of plants has not 

 till recently been so widely and systematically 

 followed up as the economic importance of the 

 subject deserves. Our knowledge, therefore, of the 

 causes and of the conditions of disease in the 

 vegetable kingdom is comparatively limited and 

 imperfect. Enough is, however, known to estab- 

 lish the general conclusion that, though there is in 

 many cases a close analogy lietween the diseases of 

 plants and animals, the pauses of disease are very 

 different in their nature in the main. While 

 bacteria and the allied Schizomycetes are recog- 

 nised as the active agents in the development of 

 disease in animals, parasitic fungi are now regarded 

 as the chief cause of disease in plants. Wet rot in 

 the potato, rot in the bulbs of the hyacinth and the 

 onion, gummosis in the tomato, yellows in the 

 peach, and pink decay in wheat may l>e cited as the 

 principal diseases of plants at present ascertained 

 to be caused by bacteria. 



Parasitic fun^i are extremely numerous, and are 

 as varied in their action and peculiar in the parta 

 they affect as they are numerous. Some attack 

 the root-, others the stem and branches, while the 

 flowers and even the several organs of reproduction 

 and the fruit are each liable to be attacked by 

 some particular parasite which induces disease. 

 They are almost always local in their action, and 

 it is very rare to find a case in which the whole 

 organism of a plant is affected in the sense that 

 man and other animals are said to be constitution- 

 ally diseased. Instances there are in varieties of 

 cultivated plants of something extremely like con- 

 stitutional proneness to disease. Certain varieties 

 of peas and of wheat are extremely liable to mil 

 dew, and to become aliortive or die of the affection. 

 But such extreme cases are regarded as evidence 

 rather of local or temporary conditions being 

 favourable to an overwhelming distribution of the 

 parasite and the consequent multiplication of the 

 lesions than of the permeation of disease which 

 takes place in the organism of animals on the 

 intriKluction of a microW into the blood. ' 



Nor is heredity so generally recognised as & 

 factor in predisposing plants to disease as it is 

 ascertained to lie in animals. The tendency already 

 alluded to in some varieties of peas and wheat, ami 

 a similar tendency to canker in some varieties of tin 

 apple, ami the greater liability of certain varieties of 

 the potato to succumb to disease than others, would 

 indeed appear to be attributable to hereditary pic- 

 disposition in the individual kinds. But it is 

 generally conceited that such peculiarities are indi- 

 cations only of constitutional weakness in the 

 variety, not of any hereditary proneness to disease. 



In the suddenness of outbreak and the rapidity 

 with which they spread when they first appear in 

 a country or locality, there is a strong resemblance 

 in some plant diseases to certain epidemics in 

 animals. And this resemblance is carried further 

 in tracing the subsequent history of notable plant 

 diseases. They appear, like epidemics in animals, 

 to exhaust their extreme virulence after a time. 

 The cases of attack may continue numerous and 



