ALBUGO (CYSTOPUS). 99 



nucleus. Swingle ('98) called attention to this body in A. Candida, 

 which he was inclined to regard as an organ of the oogonium, taking 

 some part in the delimination of the egg and the fusion of the male 

 and female nuclei. A similar body has been observed in A. bliti, A. 

 tragopogonis, and A. portulacece, by Stevens ('99), who proposed 

 for it the name " coenocentrum." In A. bliti, in which it was 

 described as structureless and unchanging, this body does not seem to 

 be so intimately associated with the sexual nuclei as in A. Candida, as 

 noted by Wager and Davis. In A. tragopogonis\\. occupies an interme- 

 diate position in size between that in A. bliti and A. Candida, where 

 it is largest. According to Davis's figures the female nucleus does 

 not become embedded in the body in question. In A. Candida this 

 body disappears during the union of the sexual nuclei or a little later. 



There is no doubt that these observers refer to the same phenome- 

 non, which is the expression of a specialized and tolerably well differ- 

 entiated portion of the cytoplasm of the oogonium. It may have to do 

 in some way with the delimination of the egg-cell and, possibly, with 

 the union of the sexual nuclei, but it certainly can not be regarded as 

 an organ of the cell or of the oogonium with morphological rank. 

 Stevens ('01) regards this body as nutritive in character and exerting 

 a chemotactic stimulus upon the sexual nuclei. 



During the changes just described the nuclei of the antheridium have 

 been undergoing division, and their number is now about twice that at 

 the beginning. The conjugation-tube has grown and pushed its way 

 through the periplasm into the plasma of the egg. A single nucleus 

 and a small quantity of densely staining cytoplasm pass from the 

 antheridium into the conjugation-tube to its apex (Fig. 35, D). The 

 tube now grows toward the centei of the oosphere, around which a 

 plasma membrane has not yet been formed (Fig. 35, E). The dense 

 mass of cytoplasm in the end of the tube becomes reduced in amount, 

 having been used up probably to form the new growing wall (Wager, 

 '96, p. 330). The growth of the conjugation-tube continues until it 

 comes into contact with the central mass of dense cytoplasm (coeno- 

 centrum) referred to in the preceding paragraphs. As soon as the end 

 of the tube comes into contact with the nucleus of the egg the male 

 nucleus is expelled and the tube immediately contracts, or rather col- 

 lapses, and is withdrawn from or absorbed by the oosphere, leaving a 

 large vacuole to mark its position (Fig. 36, F, a). The two nuclei are 

 thus left in close contact with each other, the male being slightly smaller 

 than the female (Fig. 36, F). A delicate membrane, the plasma 

 membrane, now becomes visible around the oosphere, separating it 

 from the dense surrounding cytoplasm, the periplasm. From Davis's 



