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1906] SHREVE—SARRACENIA PURPUREA 115 
_ (fig. 30). In this manner the edges of the placentae are reached 
after a course in the ovary which, for the tubes growing to the lower- 
most ovules, is as much as 6 to 8™™, and lies entirely outside the 
_ tissue of the plant in an ovary the cavity of which has direct com- 
_ munication with the external air. The epidermal cells of the placental 
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surfaces between which the pollen tubes pass are densely filled with 
_ cytoplasm; beneath them lie three layers of flattened cells of similar 
contents. Thin transverse walls are formed in the tubes near the 
_ stigmatic surface (fig. 37), and far down in the ovary, near the 
_ ovules, plugs are not infrequent in the tubes, being three to six times 
_ the diameter of the tube in length. 
The distance traversed by the pollen tubes which reach the lower- 
~ most ovules in flowers of average size, is about 4°". Provision for 
the nutrition of the tube during its growth and passage is perhaps 
made in part by the photosynthetic activity of the umbrella. Pre- 
vious to pollination the epidermal, subepidermal, and some deeper 
cells of the umbrella are filled with densely-staining, finely granular 
contents. In fresh material of the same age the contents of these 
_ cells fail to react to tests for sugar made with Fehling’s solution, a- 
_ naphthol and thymol, as well as to tests for starch. Similar contents 
_ fill the epidermal cells of the stalk of the style. The ‘course of the 
tubes as far as their entrance to the ovary is doubtless through a 
_ Strong solution of sugars. Below the point of entrance to the ovary 
_ the passage between the placental walls is probably through a film 
_ of sugary solution held there by capillarity and supplied with mate- 
als from the epidermal cells of the placental walls, which after 
pollination are highly vacuolated, in marked contrast to their con- 
dition before pollination. 
FERTILIZATION. 
The fusion of the male and female nuclei in fertilization is pre- 
ceded by the division of the endosperm nucleus in nearly all the 
embryo sacs. Fertilization takes place, then, in all ovules at nearly 
_ the same time irrespective of a difference in the development of the 
a endosperm due to the position of the ovule upon the placenta. As 
to the length of time intervening between pollination and fertiliza- 
_ tion Tam unable to give any exact data. A visit on May 24 to plants 
