464 THE AMERICAN NATURALIST. [VOL. XXXVIII. 



that the kinoplasmic membrane has any relation to these mitotic 

 figures. That is to say, there are no fibrillae to contribute sub- 

 stance to the membrane, and its development must be concerned 

 with vacuoles alone. In this respect the process recalls the part 

 played by vacuoles in the plasmodium and in certain sporangia 

 during cleavage by constriction. 



Free cell formation after the method in the egg of Ephedra 

 (Strasburger, '79), which is also likely to be found among other 

 gymnosperms, takes place during the differentiation of the em- 

 bryo cells. The cytoplasm collects around each nucleus, forming 

 a sphere (Fig. 8 g), and a wall is developed on the outside of 

 this body. Details of the process are not known, and it is not 

 clear whether the position of the membrane is determined by the 

 vacuoles that must border upon this region or whether there are 

 fibers radiating from the nucleus which might lay down a cell 

 plate around the denser protoplasm ; but the evidence favors the 

 former possibility. 



Somewhat similar conditions are presented in the egg appa- 

 ratus of many embryo sacs. In certain forms (e. g., the lily so 

 well described by Mottier, '98) the egg nucleus and synergids are 

 thickly invested by radiating fibers, and these, together with the 

 cell plates, may readily determine the position of the plasma 

 membrane that forms the cell wall. But fibers do not seem to 

 be conspicuously present in the egg apparatus of many other 

 embryo sacs (Excellent illustrations can be found among the 

 Ranunculaceae). In these cases the protoplasm collects around 

 the nuclei as dense areas bordered by vacuolar cytoplasm, and it 

 is possible that the vacuoles by fusing with one another cut out 

 these respective regions and thus determine the plasma mem- 

 branes of the egg and synergids. Such processes would extend 

 the activities of vacuoles, which accompany cleavage by constric- 

 tion in the thallophytes, to the highest groups of plants. 



It is curious that with all of the work upon the embryo sac 

 we should know less about the segmentation of the protoplasm 

 around the synergid, antipodal, and segmentation nuclei in this 

 structure than in the sporangia of the molds, the ascus, or dur- 

 ing spore formation in the Myxomycetes. 



( To be continued]. 



