12 Davis . — Spore Formation in Derbesia . 
blepharoplast in these types will show physiological connexions between 
this structure and the nucleus, and that the blepharoplast will be found 
to arise, not from the plasma membrane, but from material associated with 
the nucleus. The zoospore of Oedogonium will probably prove very 
favourable for investigation from this point of view. 
With respect to the theory of a relationship between the blepharoplast 
and centrosome, Derbesia furnishes clear evidence in the negative. In this 
type the blepharoplast is formed from a very large number of granules 
derived from perhaps a third or a fourth of the nuclear surface, all similar 
to one another and to the other granules at the bases of the numerous 
radiating protoplasmic strands. These granules cannot be centrosomes 
although they may be kinoplasmic in character. I think it is possible that 
the centrosome theory of the blepharoplast, as held by Belajeff, Ikeno, and 
Hirase, will not receive support when types are studied in which the 
blepharoplast is not developed in close association with mitosis. The 
presence of a mitosis immediately preceding the formation of sperms in 
the liverworts and ferns and the position of the developing blepharoplast at 
the poles of these spindles naturally lead to its association with a centro- 
some. There are no mitoses immediately preceding zoospore formation in 
Derbesia , or indeed in the sporangium at all, and similar conditions are also 
present during zoospore formation in Oedogojiinm and a number of other 
Algae which should be studied. The investigation of the origin of the 
blepharoplast in such forms (as also in the Cycads and Ginkgo ) will probably 
show that the blepharoplast, in these cases at least, is not the homologue of 
the centrosome as this structure is generally understood. Nevertheless, 
it must be borne in mind that the studies on spermatogenesis in animals have 
shown that the locomotor apparatus of the spermatozoid is formed in large 
part from the centrosome, and botanists have been fully justified in approach- 
ing the investigation of spermatogenesis in plants from that point of view. 
It is very important that more detailed studies on spermatogenesis in 
plants be undertaken upon such favourable types as Marsilia , certain ferns, 
the Cycads, and Ginkgo. 
It is possible that both the blepharoblast and centrosome may prove 
to have fundamental points of resemblance in their relation to kinoplasm 
investing the nucleus and to systems of radiating protoplasmic strands 
running out into the cytoplasm. The substance of the blepharoplast and 
centrosome may be similar, and their position as dynamic centres may 
be clearly analogous, but without morphological relationship. There is 
much evidence that both structures are formed at the point of convergence 
of radiating protoplasmic strands, which at certain stages of development 
are likely to prove to be streams of protoplasm bringing material to 
a dynamic centre. When such streams converge to a well-defined centre 
the whole system takes the form of an aster. Indeed there are reasons for 
