190 THE LOWER FUNGI— PHYCOMYCETES 



mitosis a sphere of dense, deeply staining, slightly granular 

 cytoplasm, several times the diameter of a single nucleus, appears 

 in the center of the ooplasm. This structure has been termed 

 the central body or coenocentrum. It is sometimes surrounded 

 by a zone of lighter staining ooplasm through which delicate 

 astral radiations pass. Though not a permanent structure 

 in the cell it is prominent for a period immediately preceding 

 fertilization. Shortly after its appearance a single female 

 nucleus is attracted by it to the center of the oosphere and 

 remains there while the other nuclei of the oosphere pass out 

 into the periplasm where they form a sphere about the ooplasm. 

 The fertilization tube carrying a single male nucleus and a 

 small amount of cytoplasm then penetrates to the center of the 

 oosphere, reaches the coenocentrum, and ruptures. The male 

 nucleus comes in contact with the female nucleus and fuses with 

 it, the fertilization tube collapses, is withdrawn from the oosphere 

 leaving a large vacuole, and the wall of the oospore is laid down. 

 The endospore is thin; the exospore is thick and at completion 

 definitely tuberculate. The supernumerary nuclei in the 

 antheridium and in the periplasm disintegrate following fertiliza- 

 tion, and the coenocentrum disappears. The fusion nucleus soon 

 divides and repeated mitoses result in the formation of about 

 thirty nuclei. Since the number of uninucleate zoospores formed 

 later in germination is slightly in excess of one hundred. Wager 

 regards the thirty nuclei as spore-mother nuclei, and feels that 

 they undergo the maturation divisions immediately before 

 swarmspore formation. There is, however, as much reason to 

 regard the two simultaneous mitoses which occur in the game- 

 tangia preceding fertilization as the reducing divisions; or from 

 analogy with other fungi the first two mitoses of the fusion 

 nucleus may well be regarded as accomplishing reduction. In 

 any case in the absence of more complete knowledge only specu- 

 lation is possible. 



In A. hliti a wholly different type of fertilization has been 

 described. In this species the oogonium contains about three 

 hundred nuclei, and the antheridium about thirty-five. The 

 receptive papilla extends far into the antheridium, and is much 

 more prominent than in A. Candida. As the content of the 

 oogonium begins to differentiate into ooplasm and periplasm all 

 of the nuclei migrate to the periphery undergoing a mitosis as 

 they pass outward. Soon they are arranged in a hollow sphere 



