PHYSIOLOGY AND MORPHOLOGY OF CALIFORNIA HEPATICA! 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 /7m- 
briaria and Targionza his figures show an early development 
of the young plant not unlike that in the case of /tzccza tricho- 
carpa. ‘The writer’s investigations relative to the germination 
of both Fossombronia and /imbriarta 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, @ przor:, 
assume that Goebel’s Predssca and ARiccéa 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 alge, 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 was 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 alge, liverworts and certain ferns, these walls 
always forming at right angles to the direction of the light rays.* 
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 | 
1 MacDougal, 1903: The Influence of Light and Darkness upon Growth and 
Development. Memoirs of the New York Botanical Garden, Vol. II. 
MOE: City, P.330- 
3 Rosenvinge, 1889: Influence d’agents exterieurs sur lVorganisation polaire 
et dorsiventral des;plantes. Revue Generale de Botanique, 1. 
* Peirce, 1906: Studies of Irritability in Plants, p. 453. 
