144 
WALTER P. THOMPSON 
6. Ovulate Flower and Megasporangium 
I. Fertile, (a) Envelopes. — The rudiment of the whole structure is 
first recognizable as an elevation just above a collar of the strobilus. 
From the periphery of this elevation a thick, many-layered envelope 
is differentiated which grows up and encloses the central protuberance 
(fig. ii). This envelope becomes the so-called perianth. After it 
has enclosed the central rudiment another and thinner envelope is 
differentiated in similar fashion. While the latter is still very small 
the depression appears which separates the third and innermost 
envelope from the nucellus (see fig. 12, in which this circular depression 
is barely recognizable). The three envelopes thus develop in acro- 
petal succession. In all the species investigated by the writer this is 
the order of development. This statement is in accordance with 
the observations of the earlier investigators (Strasburger, 25) and 
contrary to those of Coulter (7) who states that the inner envelope 
appears before the middle one. 
The inner envelope soon elongates enormously (figs. 13 and 14). 
It quickly extends beyond the middle envelope and later even beyond 
the outer one to form the so-called style. At pollination time its tip 
becomes flaring and lacerated and always holds a droplet of liquid in 
which the pollen grains lodge. Its inner structure undergoes a signif- 
icant development. All the cells except the innermost layer remain 
small and elongated parallel to the axis of the style. The cells of the 
layer lining the cavity, however, become large and elongated at right 
angles to the axis (fig. 17). Their rounded ends project into the 
cavity. Their protoplasm and nuclei become very dense and deeply 
staining (fig. 18). In fact the whole layer appears to be nutritive. 
A little below the middle a considerable chamber is formed in which 
many of the pollen grains lodge, appearing to stick first against the 
projecting ends of the nutritive cells. Here the pollen grains germi- 
nate and the tubes grow down to the nucellus. The nutritive layer 
becomes disintegrated into a granular mass by the growth of the tubes. 
After the pollen grains germinate the passage above the chamber 
closes. 
Not all the pollen grains germinate in the style. Indeed most of 
them germinate on the tip of the nucellus (fig. 35). Nevertheless 
the style is much more like that of Angiosperms than had been sup- 
posed. It not only catches the microspores but also serves to conduct 
