ZOOLOaT AND BOTANY, MICKOSCOPY, ETC. 627 



papillae. Tlie lamina and its appendages occupy different positions 

 with, respect to one another, so that the leaf may be either open or 

 closed. The entire mechanism acts in the same way as that of 

 Dioncea. 



Power of Movement in Plants.* — Sir. Darwin's book under this 

 title is an extension, as it were, of his previous treatise on climbing 

 plants. He shows that every growing part of every plant is con- 

 tinually moving round — " circumnutating " as he calls it. The 

 movements of climbing plants, the upraising and depression of leaves, 

 the movements of certain parts towards or from the light, all are 

 modifications of this circumnutatory tendency. The most novel 

 portions of the treatise are those relating to the movements of seed- 

 ling plants, the upper part of which is alone sensitive to light and 

 transmits an influence to the lower part, causing it to bend. If, 

 therefore, the upper part be shielded from the influence of light, there 

 will be no movement of the seedling, even though the lower portion 

 be exposed to the light for hours. Still more novel and remarkable 

 are the facts that Mr. Darwin brings forward with reference to the 

 movements of the radicles and minute root-fibres. These, as it 

 appears, are in constant movement, so far as the obstacles in their way 

 will permit, and it is easy to see of what use this rotating movement 

 is in enabling them to penetrate between some obstacles or to avoid 

 others. The tip of the root, moreover, is sensitive to the touch and 

 to various stimuli, and when thus excited it transmits an influence to 

 the upper part, causing it to bend from the pressed side. On the 

 other hand, if the tip be exposed to a current of watery vapour on one 

 side the upper part of the radicle bends to that side. 



The bulk of the book consists of the record of a series of elaborate 

 experiments proving the existence and nature of the movements 

 alluded to. The experiments were made by affixing to the part to be 

 examined, by means of shellac, a fine thread of glass tipped by a 

 minute dot of sealing-wax. A card with a similar black dot was 

 af&xed close by, and so arranged that on beginning an observation the 

 black dot on the glass filament and that on the card coincided in 

 position. As the plant or part of the j)lant moved, while the card 

 was fixed, the relative position of the two black dots of com^se varied, 

 and 'the degree of variation was marked upon the horizontal or 

 vertical glass plate through which the plant was observed by a series 

 of marks, which, when subsequently connected by lines, represented 

 to some extent the course of the moving object. It is probable that 

 some more accurate and " self-recording " register will hereafter be 

 devised ; but for Mr. Darwin's present purj)ose, for the mere establish- 

 ment of the facts in their broad outlines, this plan is sufficient. 



The tendency of modern investigation has been to break down in 

 many points the alleged distinctive marks between plants and animals. 

 One by one the old supposed distinctions have been abandoned, so 

 that at present the prevalent belief is that all life is essentially one, 



* Darwin, C. (assisted by F. Darwiu), 'The Power of Movement iu Plants,' 

 573 pp. and 196 figs. (Svo, Loudon, ISSO.) 



