PHYSIOLOGY AND MORPHOLOGY OF CALH-ORMA HEPATIC^ 4 



An examination of the figure referred to, however, will show 

 that although an angle was present in the young gametophyte 

 it developed in the germ-tube itself, the upper portion of which 

 lies in the direct axis of growth of the young plant, no such 

 structure as a pro-embryo being present. In his study of Fhn- 

 briaria and Targionia his figures show an early development 

 of the young plant not unlike that in the case of Riccia tricho- 

 carpa. The writer's investigations relative to the germination 

 of both Fossonihronia and Fimbriaria agree in detail with those 

 of Campbell in the forms studied by him (Figs. 22 and 23). 



MacDougal • has shown that, given the necessary intensity of 

 light, its direction will vitally influence the form and habit of a 

 living plant as well as the disposition of various organs incident 

 to its development. This being true, we might, a -priori^ 

 assume that Goebel's Preissia and Riccia spores on germinat- 

 ing take on the angular form shown in his Fig. 95 because of 

 certain external factors and, most of all, light, instead of trying 

 to account for it on grounds of heredity or of certain inherent 

 factors. In fact, Peirce,^ Rosenvinge,^ and others have experi- 

 mentally shown that in the case of certain algag, germinating 

 spores are profoundly influenced by the direction and intensity 

 of light. Eliminating so far as possible all other external factors 

 it was found that the young plants always grew towards the 

 light, while the rhizoid or the holdfast vvas negatively helio- 

 tropic. Peirce has demonstrated that in addition to this, light 

 exerts a directive influence upon the formation of cross-walls 

 in sporelings of algas, liverworts and certain ferns, these walls 

 always forming at right angles to the direction of the light ra3's.* 



With ferns and liverworts he has further shown that when the 

 long axis of the germ-tube lies in the direction of the light rays, 

 the continued growth of the young plant will be in the same 

 direction. More than this, he has demonstrated that when the 

 germ-tube ruptures the spore wall on the side away from the 



'MacDougal, 1903 : The Influence of Light and Darkness upon Growth and 

 Development. Memoirs of the New York Botanical Garden, Vol. II. 



2Loc. cit., p. 338. 



'Rosenvinge, 1S89 : Influence d'agents exterieurs sur I'organisation polaire 

 et dorsiventral des'plantes. Revue Generate de Botanique, i. 



* Peirce, 1906 : Studies of Irritability in Plants, p. 453. 



