286 BOTANICAL GAZETTE [ocTOBER 
by the annulus, a derivative of the epidermal tissue. A similar 
situation is presented by the sporangia of other vascular crypto- 
gams. Fig. 14 reproduces the situation for a species of Selaginella, 
one of the Lycopsida. In fig. 15 a microsporangium of Zamia 
muricata is represented. The spore sac is opened by an external 
annulus, precisely as in the ferns and lycopods. The epidermal 
character of the opening mechanism is clearly vouched for by the 
presence of stomata. These are visible on the upper and lower 
sides of the figure. Noteworthy in this case is the fact that the 
tracheids of the vascular bundle do not enter into the wall of 
the sporangium proper, but stop short at its base. Fig. 16 illus- 
trates a surface view of the spore sac much more highly magnified, 
making clear the position and organization of the stomata. If we 
compare the condition presented by the sporangia of cycads and 
vascular cryptogams with that found in Ginkgo, a remarkable 
contrast in the character of the opening mechanism is found. In 
the lower forms the apparatus for the dehiscence of the spore sacs 
is known as an annulus and is derived from modified epidermal 
cells. In the case of Ginkgo, on the other hand, no annulus is 
present, and the opening of the sporangium is provided for by an 
internal mechanism, obviously an adjunct of the fibrovascular and | 
transfusion tissues, commonly known as the mechanical layer. 
It is now convenient to consider the situation in the seed- 
bearing forms which lie above Ginkgo in the scale. The first group 
to be discussed in this connection is the Coniferales. One of us 
has pointed out in numerous recent communications that the 
Abietineae have the strongest claim to a primitive position among 
the coniferous subtribes. This view is as yet not accepted by the 
greater number of paleobotanists, but seems to be based on evi- 
dence which in the long run is destined to prevail. A most inter- 
esting confirmation of the hypothesis of the primitive character 
of the Abietineae is provided by their microsporangial resemblances 
to Ginkgo. In the first place, the organization of the male cone of 
Ginkgo is similar to that of the Abietineae, since it is compos 
of sporophylls each bearing two sporangia. One of us has pointed 
out’ that the spoons grains of Ginkgo possess wings comparable to 
5 Jerrrey, E. C., Spore conditions in hybrids and the mutation hypothesis of 
DeVries. Bor. dae 58:322-336. pls. 22-25. 1914. 
