438 
Hill and de Fraine. — On the 
Finally, it may be remarked that as this particular series of papers is 
already somewhat detailed and lengthy, it has been considered desirable to 
make little or no mention of histological features of the Cycadaceae, more 
especially of the vascular bundles, here. They may, if necessary, form the 
subject of a separate communication. 
Macrozamia. 
Macrozamia spiralis . 
The form of the seedling closely resembles that of Ginkgo and is 
illustrated in Fig. 4, PI. XXX. There are two hypogeal cotyledons which, 
throughout their existence, remain embedded in the endosperm of the seed ; 
they are of unequal size, and the larger one is also often slightly longer, its 
tip sometimes being folded over the free end of the smaller. 
The seed-leaves are very closely adpressed by their ventral surfaces ; 
at the apex, and a little below, the epidermis of each member forms a line 
of demarcation, but at a slightly lower level the fusion appears to be quite 
complete, the ventral epidermis can no longer be distinguished, and a trans- 
verse section has all the appearances of a section of a stem. 
At a still lower level the boundary line again appears and, towards 
their bases, the seed-leaves partly separate to form a cotyledonary tube 
which encloses the plumule. 
As regards structure little need be said. Stomata, sunken below the 
general level of the epidermis, have been observed, and they are restricted, 
as far as has been seen, to the dorsal surface where the cuticle is fairly well 
pronounced and thicker than on the ventral surface. The internal structure 
resembles very closely that of Ginkgo. The compact mesophyll is homo- 
geneous, and its parenchymatous cells are densely packed with starch 
grains. Secretory cells are abundant, and also mucilage canals of a large 
size ; the number of these latter varies, about five in each seed-leaf are 
present. 
The vascular bundles are not particularly large, and they vary in 
number in each seed-leaf ; the smaller cotyledon generally has one less 
than the larger, which usually has five ; six, however, were observed in one 
case. The vascular strands are very markedly mesarch in structure ; most, 
in some cases practically all, of the metaxylem is centripetal. 
At the extreme apex of each cotyledon there is often but one vascular 
strand consisting of a broad tangentially elongated mass of tracheides but 
no phloem ; this strand, as it is traced downwards towards the base, quickly 
divides up into four, five, or six bundles, according to the size of the 
cotyledon, and phloem is differentiated. The number of bundles thus 
produced generally remains constant, so that five strands enter the hypo- 
cotyledonary axis from one seed-leaf and four from the other. But in one 
case it was observed that the larger cotyledon had six strands and the 
