645 
Ovule of Boivenia spectabilis. 
The great point of difference between Trigonocarpus and the Cycad 
seed is in the degree of union of nucellus and integument, but this does not 
seem to be a serious obstacle in the general argument. Oliver 1 has pointed 
out that the free or fused character of the nucellus is probably determined 
by the method of growth of the ovule, and one assumes that in these two 
seeds the region of growth in the one case has been apical, in the other 
basal. Such a difference of growth, then, would account for the greatest 
feature of dissimilarity between the seeds of Trigonocarpus and the Cycads. 
The general structure of the ovule of Bowenia , therefore, in respect to the 
integument and vascular supply, as well as the pollen- chamber, points 
to a very close connexion with seeds of the Trigonocarpus affinity. 
In conclusion I should like to express my thanks to Professor W. H. 
Lang, F.R.S., for the greater part of the material on which this investiga- 
tion is based, the facilities he has given me in his laboratory, and his help 
and criticism during the progress of the work. 
Summary. 
1. The general development of the ovule of Bowenia is found to be 
similar to that of other genera of Cycads. 
2 . The embryo-sac arises from the lowest of a row of three cells, which 
are differentiated from the mass of sporogenous tissue. Free nuclear divi- 
sion proceeds in the embryo-sac, and during the subsequent growth the sporo- 
genous tissue serves as a nutritive layer. This layer is used up by the time the 
prothallus is formed, i. e. at an earlier period than in other genera of Cycads. 
3. The pollen-chamber forms by a solution of the tissue in a region of 
the nucellus previously recognizable by the arrangement of its cells. It has 
been distinguished into upper pollen-chamber , which developed first, and 
serves as a storage place for the pollen on entering the ovule, afterwards 
becoming hard and shrivelled ; and the lower pollen-chamber , a larger cavity 
forming later into which the pollen-grains pass, and where they develop 
the spermatozoids. 
4. The male gametophyte consists of two prothallial cells and a large 
terminal, generative cell with large nucleus and a pair of blepharoblasts. 
From this one stage observed it is evident that development is similar to 
that described in Zamia. 
5. The vascular supply of the ovule is derived from one foliar bundle 
of the sporophyll, and consists of an outer ring of seven to nine unbranch- 
ing bundles, collateral with mesarch xylem, which lie in the outer part 
of the integument ; and an inner series of concentric bundles which branch 
frequently. The most interesting point of the vascular supply is that in 
1 Oliver ; The Ovules of the Older Gymnosperms. Annals of Botany, vol. xvii, 1903. 
