CHAPTER F. COMPARATIVE REVIEW. CHYTRIDIEAE. 163 



Euglenae which they. encounter. In this way a much-branched plant is formed with 

 hair-like terminal branchlets, which connect with the larger main stems and through 

 these with the body of the original spore ; the latter has grown in the meantime into 

 a large round or elongated vesicle at the expense of the Euglenae, which have been 

 exhausted by the rhizoids. When it has reached a certain size, varying according to 

 the food which has been supplied to it, it shows itself in many specimens to be a 

 sporangium, or, if the term is preferred, a prosper angium. It grows out at one spot 

 into a bluntly and irregularly cylindrical -thick tube with a delicate membrane, into 

 which the whole of the protoplasm passes, and is at once divided into swarm-spores 

 (Fig. 75 C). This process of development may be repeated for many generations, and 

 leads to an immense multiplication of individuals if there is a sufficient number of 

 Euglenae within reach. When this has taken place, the course of events changes. 

 The young plants remain for the most part small and become gametes, which con- 

 jugate in pairs, each pair forming a zygospore, and these behave as resling-spores. 

 The two conjugating gametes of a pair (Fig. 75 Z>) have no definite position or 

 distance with respect to one another, and are similar in form to the non-conjugating 

 plants. The one (3), which from the processes to be described may be termed the 

 supplying gamete (abgebende Gamete), has usually a round and larger body, but shows 

 no other apparent difference before contact with the other (a], the receptive gamete 

 (aufnehmende Gamete). The latter usually continues to be smaller, and often very 

 small, and puts out rhizoid branches, and if one of these, after longer or shorter 

 growth, encounters a supplying gamete it applies its extremity to it as a conju- 

 gating tube (s) and increases in thickness while it ceases to increase in length. 

 The membrane between the conjugating tube and the supplying gamete disappears 

 at the point of attachment, and an open communication between them being thus 

 established, the whole of the united protoplasm of both gametes passes into an 

 enlargement of the conjugation-tube close to the point of attachment ; the swelling 

 gradually expands into a spherical vesicle, and being delimited by a membrane after 

 receiving the protoplasm becomes a thick-walled zygospore (E, s). The outer wall 

 of the zygospore assumes a pale yellow colour, and in some cases continues smooth, 

 in others is covered with short spikes, which begin to form at the same time as the 

 enlargement in the tube. The whole process of forming a zygospore from the 

 attachment of the conjugating tube to the maturation of the zygospore was com- 

 pleted, in the case observed by Nowakowski, in about 6-7 hours. 



A few instances are known of the conjugation of 2-3 receptive with one supplying 

 gamete and of the consequent formation of 2-3 zygospores. The zygospore, as has 

 been already said, is a resting-spore. It germinates when its resting time is over and 

 produces a zoosporangium like the non-conjugating plants. 



Polyphagus therefore is essentially characterised by the gametes with their 

 rhizoids, the mode of forming the zygospores, and the production of the zoo- 

 sporangium or of swarm-cells from it. It may be assumed to be possible for these 

 swarm-cells to develope directly into gametes ; but an indefinite number of generations 

 of non-conjugating plants are in fact interposed between two successive gamete- 

 generations. The gametes in each pair behave differently in conjugation, as has 

 been shown, and the species is dioecious. Which of the two should be called the 

 male and which the female is not easy to determine, and must not be further discussed 



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