Cytologie und Befruchtung. 295 



schwankt zwischen 2,8 und b,\^lQ, die absohite Festigkeit zwischen 

 5,03 und 10,1 kg pro qmm. Küster. 



Webber, H. J., Spermatogenesis and Fecundation of 

 Zamia. (U. S. Dept. of Agriculture. Bureau of Plant In- 

 dustry. Bulletin No. 2. p. 1 — 100. Pls. 1—7. 1901.) 



Two species growing in Florida were studied, Zamia flori- 

 dana DC. and Z. pumila L., both of which have, heretofore, 

 been incorrectiy referred to Z. Integrifolia Jacq. 



The development of the pollen grain was not foilowed in 

 detail but it is probable that there is an evanescent prothallial 

 cell. Aside from this and the tube cell, the mature pollen 

 grain contains two other cells, the inner most of which gives 

 rise to the stalk and body cells while the other reinains as a 

 persistent prothallial cell. Both the prothallial cell and the 

 stalk cell become filled with starch and the former arches into 

 the latter, sometimes giving the impression of one cell entirely 

 surrounded by another. The blepharoplasts first appear in the 

 body cell (central cell) and are formed de novo from the 

 cytoplasm. They are at first very small, being scarcely more 

 than points where a few radiating filaments converge, but as 

 they increase in size, a surrounding membrane and vacuolated 

 Contents can be differentiated. Shortly before the division of 

 the body cell they reach a diameter of 18 — 20 ,«. In the 

 division of the body cell, the nucleus passes through a synapsis 

 stage which is regarded as normal and not due to reagents. 

 The spindle is developed while the nuclear membrane is still 

 intact and is apparently entirely of nuclear origin and none 

 of the fibers have any connection with the blepharoplasts. 

 During the equatorial plate stage, the blepharoplasts break up 

 and in an early anaphase the contents have entirely disappeared, 

 while the outer membrane soon breaks up into numerous 

 granules which, during the development of the cell plate, begin 

 to fuse, thus forming the cilia-bearing band. At first, the band 

 is located in the cytoplasm midway between the nucleus and 

 the periphery of the cell but it ultimately moves out and becomes 

 appressed against the plasma membrane, where it forms a 

 helicoid spiral of from five to six turnes. The entire spermatid 

 is metamorphosed into a spermatozoid, there being no diffe- 

 rentiation of a spermatozoid within a mother cell. The mature 

 spermatozoids are the largest known . in any plant or animal, 

 being visible to the naked eye. They move mainly by means 

 of cilia but there is also an amoeboid movement of the spiral end. 



In fertilization the entire spermatozoid enters the egg, but 

 the nucleus soon escapes, leaving the ciliferous band in the 

 Upper part of the egg cytoplasm. The nucleus moves on and 

 unites with the egg nucleus. There is a fusion of cytoplasm 

 with cytoplasm and nucleus with nucleus. 



