628 SUMMARY OF CURRENT RESEARCHES RELATING TO 



and that its manifestations are exerted tlirougli the medium of 

 machinery fundamentally identical in character. In accordance with 

 these views Mr. Darwin points out the resemblance between the 

 movements of plants and many of the actions performed unconsciously 

 by the lower animals, the most striking illustration being in the kind 

 of imperfect reflex action which is shown to occur when a certain 

 portion of a jilant is stimulated by a touch or otherwise, the influence 

 being transmitted from the point of contact to some other point, which, 

 as a direct consequence of this transmitted influence, moves just as the 

 telegraph needle moves when a current is generated in the far-off battery. 

 " It is hardly an exaggeration to say," remarks Mr. Darwin, " that 

 the tip of the radicle thus endowed, and having the power of directing 

 the movements of the adjoining parts, acts like the brain of one of the 

 lower animals : the brain being seated within the anterior end of the 

 body, receiving impressions from the sense organs, and directing the 

 several movements." 



Auxotonic Movements of Vegetable Organisms.* — The term 

 auxotonic is applied by de Vries to the movements caused by an 

 augmentation of the turgidity of an organ which is not followed by 

 contraction, as in heliotropism, geotropism, nutation, epinasty, and 

 especially in the movements of tendrils ; allassotonic to those in which 

 the augmentation of tui'gidity alternates with a diminution of volume, 

 as in the movements of the sensitive plant and of the stamens of the 

 Cynaracefe. He now investigates the problem of the part played by 

 turgidity and by intussusception in the phenomena of auxotonic 

 curvatures of multicellular organs. 



The general result of his experiments is stated by de Vries to be 

 that the cause of auxotonic curvatures is an augmentation of the 

 force of turgidity in the cells on the side which subsequently becomes 

 convex. This augmentation causes the cells on that side to absorb 

 more water, and in consequence to increase in size ; thus originating 

 the curvature. The enlargement of the cells causes a distension of 

 the cell-walls, and this promotes intussusception ; and the curvature 

 thus becomes permanent. 



Irritation determines a production of osmotic substances in the 

 parenchymatous cells; and this production is the more abundant, the 

 nearer the cells are to the point of irritation. The commencement of 

 the epinastic movement is caused by the passage of substances by 

 osmose into the parenchyma. In multicellular organs which are in 

 process of growth, specific gravity and light, as well as other exciting 

 causes, bring about curvatures by accelerating endosmosis on one 

 side of the organ, which determines the increase in length. Among 

 the osmotic substances which give rise to tui'gidity in the cells 

 of plants, the author considers vegetable acids to play the principal 

 part ; the unilateral acceleration of growth, due to external causes, 

 being dependent on the acceleration of the production of these 

 acids. 



As stated by Sachs, the geotropic and heliotropic movements of 



- Arch. Need. Sci. exact, et uat., xv. (1880) pp. 295-312. 



