No. 450.] STUDIES ON THE PLANT CELL. 



the spores of an ascus, the oospore of the Peronosporales, the 

 embryo cells of Ephedra, and probably other gymnosperms, and 

 in some cases seemed to be exemplified in the conditions pre- 

 sented by the egg and synergids and the antipodals of the embryo 

 sac. 



Spore formation in the ascus is known through the studies of 

 Harper ('97 and '99). After the final divisions in the ascus the 

 nuclei lie in the cytoplasm, each with an aster at its side (Fig. 

 8 3). A delicate prolongation carries the aster with its cen- 

 trosphere away from the main body of the nucleus {e, i). The 

 rays of the aster now bend over and grow around the nucleus, 

 presenting an umbrella-like figure {e, 2). They finally meet on 

 the opposite side, and thereby cut out a portion of the cytoplasm 

 which is included in the spore. The substance of the aster 

 fibers forms the basis of a kinoplasmic film which becomes the 

 plasma membrane of the ascospore and develops the spore wall 

 externally after the usual method. This peculiar activity of an 

 aster is unparalleled in plant or animal cells. 



Oogenesis in the Peronosporales has been described in some 

 detail by several authors, but the process has not generally been 

 called free cell formation. Yet at the end of the process the 

 oospore, enveloped by periplasm, lies free in the oogonium. In 

 the beginning the ooplasm gathers in the center of the oogonium 

 as a denser alveolar region around that peculiar protoplasmic 

 body (generally present) the coenocentrum. This accumulation 

 forces the vacuoles, together with most of the nuclei, to the 

 periphery, where they lie in a sort of protoplasmic froth next 

 the cell wall and constitute the periplasm. The spore wall de- 

 velops at the boundary of the ooplasm, so that it lies close to the 

 large vacuoles (Fig. 8 /) in the periplasm. There must be an 

 accumulation of kinoplasm, perhaps from the plasma membranes 

 of numerous vacuoles, to form a delicate layer between the two 

 regions of the oogonium. This layer of kinoplasm probably 

 splits along the line of vacuoles between the ooplasm and pen- 

 plasm, for the primary walls are certainly established between 

 two plasma membranes, because the secondary layers are added 

 to it from both sides. Nuclei in division frequently he very 

 dose to the boundary of the o5plasm, but there is no evidence 



