BOTANY: C. J. CHAMBERLAIN 
89 
genus, Encephalartos, seem comfortably distinct, while others are so 
variable that one could identify herbarium specimens with more assur- 
ance than he could plants in the field. 
An experimental study of variation in cycads is not attractive. Dioon 
edule probably reaches an age of fifty years before it produces cones; 
Macrozamia Moorei has been known to cone at twenty years; some 
species of Zamia may cone at ten years, or even less; but the succession 
of generations is too slow for any experimental work involving the whole 
life history. SeedUngs of all the genera and many of the species are 
growing at the University of Chicago and it is evident that there is 
considerable variation in the seedlings from a single cone. Some work 
in hybridization is being attempted and one might reasonably hope to 
see results if any should appear in the first generation. 
In comparing Paleozoic, Mesozoic and living members of the phylum, 
it is evident that the Mesozoic forms are larger than the Paleozoic, and 
that the Hving forms are still larger than the Mesozoic. Some of the 
seeds of the Paleozoic forms were very small, but some were larger than 
any yet known in the Mesozoic, yet none even approached the large 
seeds of some of the living cycads. Cones of the Bennettitales can be 
carried in the pocket, but some of the cones of living cycads reach a 
weight of ninety pounds. While the sperms of the fossil forms have 
never been identified with certainty, the structure of the ovules makes 
it certain that they could not have been nearly so large as those of the 
Hving cycads. On the whole, there has been an increase in size as we 
pass from the Paleozoic to the living forms. 
In all the living Gymnosperms, the development of the female gameto- 
phyte begins with a series of free nuclear divisions which is followed 
by cell formation. Undoubtedly, the lowest seed plants came from 
heterosporous Pteridophytes, and it is more than probable that these 
heterosporous Pteridophytes of the Paleozoic had female gemetophytes 
beginning with free nuclear division, although the earliest heterosporous 
forms, just emerging from the homosporous condition, probably had 
female gametophytes in which all nuclear division was accompanied 
by the formation of walls. No homosporous form, either living or fossil, 
shows free nuclear division at this stage in the life history. Free nuclear 
division came with the increase in the size of the spore, and the extent 
of the free nuclear period is more or less correllated with the size of the 
spore. In the large megaspores of Dioon there may be thousands of 
free nuclei before wall formation begins; in the smaller megaspores of 
Zamia, only hundreds. 
