328 KirkKwoop: PoLien-TuBE IN CUCURBITACEAE 
some other route, 7. ¢., traversing the tissues of the funicle and 
integuments. Such conditions have been observed in Cucurbita 
and Alchemilla.® 
In its course from the stigma to the ovule, the pollen-tube may 
follow a canal through the style where such is available, and inter- 
cellular spaces as well, or it may bore through a considerable 
amount of cellular tissue, which it may or may not affect injuri- 
ously. Its course is usually a direct one and the direction of its 
growth is often influenced mechanically by the structure of the 
ovary as well as by the distribution of nutritive materials in what has 
been called conducting-tissue. The influence of the latter as a 
directing agent has received some attention at the hands of 
Miyoshi”,” and others whose work we will discuss more fully 
later, but the results from various sources go to show that in con- 
sidering the growth of the pollen-tube we are dealing with prob- 
lems of chemotropic irritability and the action of stimulating 
substances whose distribution is indicated largely by anatomical 
features. 
While the pollen-tube in angiosperms is ordinarily devoid of 
branches, a few cases have been observed in which the tube has 
divided into a number of branches after having reached the ovule. 
Hofmeister ™, describes the branching of the tubes in Pothos and 
Hippeastrum, and in the Amentiferae it has been observed in Cory- 
lus, Carpinus*, Juglans *, Hicoria (Carya)*, Cuercus* and several 
others. It occurs also in Cucurbita as described by Longo”, and 
observed by the author. That the branching is associated with 
the function of absorption has been the accepted view, and the 
observation of Longo that the branching is in a definite relation to 
the presence and distribution of starch in adjacent tissues supports 
this opinion. 
Numerous observations have been made on different plants as 
to the time consumed by the pollen-tube in traversing the distance 
from the stigma to the embryo-sac. This has been found to vary 
within wide limits and to be dependent upon no fixed principle ex- 
cept that the immediate approximation of the germ cells is corre- 
lated with their degree of maturity. In certain herbaceous plants 
the time required varies from eighteen hours (Limnocharis*) “ 
several days (Crocus, Arum) and even much longer, as in certain 
