REPORT OP COMMITTEE ON PUBLICATION 135 



represents the antheridium as a long, slender thread partially encircling 

 the oogonium. 



Briefly stated the nuclear history of the oogonium of P. alpinum is as 

 follows. First, there is a single mitotic division, after which all of the nuclei 

 but one migrate to the periphery. Simultaneously there appears at the 

 center a small dense body which seems to attract the single remaining 

 nucleus to it. This is considered by Rosenberg to be the coenocentrum. 

 Following this, another mitosis of the central nucleus occurs, which does 

 not, however, occur in all of the nuclei at the periphery. One of the sister 

 nuclei at the center then migrates to the periphery and gradually disinte- 

 grates. At this time one nucleus from the antheridium passes to the center 

 of the oogonium and after a time fuses with the female nucleus. 



In Plasmopara viticola, certain of these stages have been observed. In 

 many instances a single, well-developed nucleus occurs at the center near a 

 well-defined, denser, body, the coenocentrum (PI. IV, figs. 3 and 4) while 

 outside of the partially developed oospore wall are numerous irregular, 

 darker-staining bodies which may be interpreted as disintegrating nuclei 

 (PI. IV, figs. 3 and 4). At times there may be seen two or more nuclei 

 within the developing oospore but the fully matured oospore contains only 

 a single nucleus without the accompanying coenocentrum (PI. IV, fig. 6). 



The writer has never observed an antheridium in connection with the 

 more advanced stages of development of the oospore in the many hundreds 

 of sections obtained. This fact is amenable to two interpretations, either 

 that these oospores develop apogamously or that the antheridia very quickly 

 disintegrate. 



The protoplasm of the oospore is granular, rather yellowish brown and 

 filled with numerous, refringent globules. At times the entire center is 

 occupied with a large, round, hyalin area, having the appearance of a large 

 vacuole. The oospores are from 25 to 35/u, in diameter. The inner wall or 

 endosporium of the oospore is smooth, colorless and relatively thick. This 

 wall is formed about the oosphere immediately following fertilization. It is 

 apparently a deposition from the protoplasm (PI. IV, fig. 5). Surrounding 

 the endosporium are the disintegrating remnants of nuclei lying in the 

 periplasm. It is probable that the periplasm contracts about the endosporium 

 thus forming the irregular, brown exosporium. The oospore lies within the 

 thickened persistent, oogonial wall. The writer has seen many oospore-like 

 bodies, having spiny walls but since they are as frequently on the outside 

 of the leaf as within it is apparent that they are not spiny forms of the 

 oospores of Plasmopara viticola. 



As has been pointed out by the writer (1913) there were many unsuc- 

 cessful attempts to germinate the oospores of Plasmopara viticola but, not- 

 withstanding these failures, two theories were evolved as to the probable 

 method of germination. On the one hand we find Millardet (1883), Frechou 

 (1885), Richon, Viala (1893) and others who considered that zoospores were 

 formed directly from the protoplasm of the oospore. On the other hand, 

 Cornu (1882) and Prillieux (1883) were equally certain that the oospores 

 produced a typical conidiophore bearing conidia. 



The writer (1913) published an account of germination by means of a 

 promycelium bearing a single conidium (PI. Ill, fig. 11). Shortly afterwards. 



