90 
BOTANY: C /. CHAMBERLAIN 
That the theory, just expressed, is correct, is indicated by the early 
development of the sporophyte in Gymnosperms. The eggs are large, 
and — with two or three exceptions — fertilization is followed by a period 
of free nuclear division before walls begin to appear. In the two or 
three exceptions, the egg is small, and the first division of its nucleus is 
followed by the formation of a wall. In all Angiosperms, the egg is 
small and a wall follows the first division of its nucleus. 
Thus we have a series beginning with the homosporous Pteridophytes 
in which a wall always followed the first division of the spore, free 
nuclear division appearing somewhere, as heterospory was attained and 
the megaspore increased in size; the free nuclear period becoming more 
prolonged in the larger megaspores of the Gymnosperms, then culmi- 
nating and beginning to decline in the cycads. The series is even more 
striking in case of the embryo, since there is the same increase, cul- 
mination and decline of the free nuclear period and a few Gymnosperms, 
together with all Angiosperms have come back to the original condition 
in which a wall follows the first nuclear division of the egg. 
Some of the microscopic details are remarkably constant, e.g., in 
the pollen tube of all the genera the prothallial cell presses deeply into 
the body cell. The cycads can be distinguished from all other living 
seed plants by this cytological character. In all the genera, two blepharo- 
plasts appear in the body cell and, in the two sperms derived from it, 
develop into coiled bands bearing thousands of cilia by means of which 
the sperm becomes a vigorous swimmer. Since these details are so 
uniform, they must antedate the differentiation into the modern genera. 
On the other hand, there are characteristic differences in the pollen 
tubes and their contents, so that the pollen tube structures will not only 
distinguish the family from other seed plants, but will distinguish the 
genera from each other. 
The foregoing paragraphs are intended to indicate the drift of a few 
phases of an investigation which has been in progress for more than 
ten years. So far, only scattered descriptive sketches have been pub- 
lished, but all the genera and many of the species have been studied in 
the field and material has been collected for detailed studies of prac- 
tically all phases of the life histories. Besides, obliging correspondents 
in Cuba, Mexico, Australia and Africa are constantly sending field 
notes, photographs and material, so that, in time, the interrelationships 
of the genera and the origin of the family may be cleared up and some 
opinion may be ventured in regard to phylogenetic characters and their 
gradual modification. 
