1897] ZAMIA AND GINKGO 229 
of an aster, but in no case has any body been noticed which could 
be considered a centrosome. Hirase, in his studies of Ginkgo, 
states that he was unable to find any indication of a centrosome 
either in the first or the later divisions of the oosphere.® It should 
be remembered in this connection that Overton’ states that in 
Ceratozamia the pollen mother cells and endosperm shortly after 
the formation of the free cells in the embryo sac are very 
favorable objects for the study of the centrosome. It would 
seem, however, from Hirase’s studies on Ginkgo, my own on 
Zamia, and the recent cytological studies at the Bonn Botanical 
Institute, that Overton may possibly have been mistaken. 
In the generative cell of Ginkgo biloba, according to Hirase,* 
two “‘attractive spheres” occur which are visible without stain- 
ing. These organs are unquestionably the same as the centro- 
some-like bodies which I have described in Zamia. Hoping thus 
to obtain further information as to the nature and origin of these 
bodies, I have made a study of the early stages of the develop- 
ment of the pollen tube of Ginkgo. In developing fruits col- 
lected June 12, the pollen was found to have germinated and 
formed a tube about as long as the diameter of the pollen grain. 
In this stage (jig. 4) the vegetative nucleus in all cases exam- 
ined had already wandered into the tube and was commonly 
found near its distal end. The stalk cell and generative cell, 
which, as Strasburger has shown, are formed in the pollen grain 
before pollination, had at this period increased only slightly in 
size, and were yet much smaller than the vegetative nucleus. 
The generative cell in this stage is crescent shaped and projects 
into the center of the pollen grain. The nucleus is about 5.6 in 
diameter and occupies about one-half of the cell. The nucleus 
of the stalk cell is somewhat smaller, while the vegetative 
nucleus is much larger, being about 10.5m in diameter. 
Etudes sur la fécondation et Vembryogénie du Gingko biloba, Journ, of the 
Col. of Sci, Imp. Univ, Japan 8 : 307 
7 Ueber die Reduction der Poaialdain | in den Kernen der Pflanzen. Viertel 
jahrschr, d, naturforsch. Ges. in Ziirich 
38 : 178. ; 
* Notes on attraction spheres in the pollen cells of Ginkgo biloba. The Botanical 
Magazine 8 : 359. 
