236 BOTANICAL GAZETTE [MARCH 
chromosomes were estimated to be thirty-two in number, and in the endo- 
sperm enough was observed to indicate that the number was approximately 
sixteen.—J. M.C, 
ORIGIN OF THE OVULE.— Paleobotanical evidence for the origin of the 
ovule is accumulating with remarkable rapidity. In discussing the ovules of 
the older gymnosperms, F. W. Oliver*® has described some most significant 
structures. The two ordinary types of unassigned paleozoic seeds are called 
for convenience Radiospermae and Platyspermae, the former including radi- 
ally symmetrical seeds, the latter flattened ones. The simplest form is known 
as Stephanospermum (a radiosperm), in which the nucellus stands up freely 
within the integument: the apex of the nucellus is occupied by an extensive 
pollen-chamber ; and “the chalazal strand of tracheids expands at the base 
of the nucellus into a tracheal plate, the margins of which are continued in 
the wall of the nucellus right up to the pollen chamber, the floor of which is 
paved with tracheids.” The pollen grains are multicellular, and apparently 
liberated free-swimming sperms. The tracheal mantle of the nucellus is 
thought to be a mechanism for bringing water to the pollen-chamber, to be 
of use to the swimming sperms. This promiscuous liberation of swimming 
sperms is thought to be reminiscent of a heterosporous pteridophyte. 
Among the platysperms (Cardiocarpus as type) there is the same tracheal 
plate at the base of the nucellus, from which tracheal strands extend into the 
walls of the nucellus at least as far as the separation of pre and 
nucellus. In this case the tracheal mantle, so far as known, is not so 
plete as in Stephanospermum. Moreover, the pollen grains are lee 
but the cell-group by no means fills the entire grain. It is evident that t 
platysperms approach the cycads much more nearly in these particulars ae 
do the radiosperms 
One of the most striking seeds, however, is that of Lagenostoma, from the 
lower Coal Measures. The integument and nucellus are free from one another 
only in the region of the pollen chamber, from the floor of which a conical 
mass of nucellar tissue rises, plugging up the micropyle (a structure, by the 
way, resembling that described by Hirase in Ginkgo), leaving the cavity of 
the pollen chamber a circular crevice. Surrounding the pollen chamber is 
the very complicated integument, consisting of an outer zone of heavy tissue, 
d an inner zone of large chambers separated by strong radiating plates. 
The internal angle of each chamber is convex, the inner wall of the integu- 
ment thus forming a fluted membrane known as the “canopy.” It seems 
that each of the large, vertical chambers of the integument was occupied by 
soft parenchyma, through which there ran longitudinally a single tracheal 
strand. In this case, also, the pollen grains were filled with tissue, indicating 
free-swimming sperms, and the more or less complete tracheal mantle would 
8 OLIVER, F, W., The ovules of the older gymnosperms. Ann. Botany 17: 45I- 
47% pl. 24. 1903. 
