CYCADALES 31 



ence of numerous free nuclei distributed through the cytoplasm. 

 He naturally inferred that these were derived by repeated 

 nuclear division from the oospore nucleus. Ikeno observed the 

 first division of this nucleus, and has called attention to certain 

 peculiarities connected with it — peculiarities which are chiefly 

 suggestive in being found also in Ginkgo and in Pinus. The 

 first nuclear spindle is the largest one which appears during free 

 nuclear division, and its axis is always inclined to the long axis 

 of the archegonium. Whether this position is significant or 

 not remains to be seen, but the fact that it is also observed in 

 Ginkgo and Pinus suggests that it is worthy of record. The 

 fibers of this primary spindle do not converge as they do in all 

 subsequent ones. As a consequence, this spindle is very broad 

 in outline, really rectangular, while all subsequent spindles are 

 distinctly bipolar. A further point of interest in connection 

 with this spindle is that there are no centrosomes, or centrosome- 

 like bodies, or even polar radiations connected with it. It would 

 seem, therefore, that there is no organ which might be regarded 

 as the lineal descendant of the blepharoplast, which was so promi- 

 nent in the sperm series. The subsequent bipolar spindles show 

 the ordinary radiations, but no bodies at the poles. 



Free nuclear division proceeds with rapidity and in simul- 

 taneous fashion until the nuclei become very abundant. Ikeno 

 calls attention to the fact that at this time the structure of the 

 cytoplasm of the central region changes. It becomes at first vac- 

 uolate, and then completely disorganizes, the niiclei imbedded in 

 it sharing the same fate. The remaining cytoplasm becomes 

 parietal, massing somewhat towards the bottom of the spore. In 

 this parietal layer the nuclei are imbedded, being equidistant 

 from one another and forming usually a single layer, but at the 

 base they are more massed. In this position the nuclei con- 

 tinue to divide and reach large nmnbers, when cell walls begin 

 to appear. An interesting fact in connection with this division 

 of nuclei, when in the parietal position, is that some of the free 

 nuclei which are nearest the neck end of the oospore divide ami- 

 totically, but this tendency seldom reaches into the deeper re- 

 gions. As a result of this development the proembryo becomes 

 a sac, somewhat thickened at the base, but with the wall com- 

 posed of one or at most two layers of cells. At this point the 

 work of Ikeno stops, and beyond it Treub gives very little detail. 



