BEHAVIOR OF THE POLLEN TUBE 95. 
region of the micropyle it passes beyond the surface of the epi- 
thelium (£g. 6). It then glides along the surface a short distance 
and then passes between the conductive epidermis and the integu- 
ment (text fig. 1). Ultimately it finds the micropyle and travels 
along it to the embryo-sac. 
Two points of importance are to be noted at this point, the en- 
tirely or almost entirely intercellular path of the pollen tube, and 
the direction of its path which is not in the direction of least re- 
sistance, but at right angles to the longtudinal axis of the cells of 
the conducting tissue. | 
During this part of its course, that is, as it is passing through 
- the fusion tissue and the strophiolar conductive tissue, the pollen 
tube as above pointed out not. infrequently branches (fg. 7). 
Nawaschin has noted a similar tendency on the part of pollen 
tubes in the Birch (11, p. 22), to branch “wo das betreffende 
gewebe keine deutliche Anordnung seiner Zellen in longitudinalen 
Reihen aufweist.” When in the strophiolar conductive tissue, the 
pollen tube shows more or less inability to pursue a path which is 
constantly at right angles to the component cells. It may then 
slip out to the surface. This happens most frequently in Richard- 
sonia in the neighborhood of the micropyle where there is little or 
no pressure exerted upon the strophiole by the adjacent structures. 
In Diodia teres where the strophiole in the micropylar region is 
tightly wedged between the ovule and the wall of the ovary, the 
pollen tubes take constantly a deeper course (text fig. 5). These 
phenomena lead to the suggestion that the cause which has brought 
about the habit of intercellular growth in the pollen tube is a me- 
chanical one, and this factor may probably be called upon to ac- 
count for the behavior of the pollen tube in many forms. We 
have in mind such cases as occur, for example, in the Cannabinaceae 
of which Zinger (23) has given an account. According to this 
author, the intercellular node of growth is of phylogenetic signifi- 
cance, and, by means of such interpretation, brings his view into 
line with that of Nawaschin, who has vigorously supported the 
contention that the behavior of the pollen tube in the Amentiferae 
is inherited from their ancestral forms, and has endeavored, on this 
theory, to connect the lower Angiosperms with the Gymnosperms 
A discussion of this question is not pertinent here, but it may be 
