6o 



INTRODUCTION TO THE STUDY OF FUNGI 



protoplasm, and gradually enlarge, until they resemble a spindle- 

 shaped connective of the two hyphae. A septum is soon 

 formed across the suspenders near the upper extremity, cutting 

 off a discoid cell from each, which are separated from each 

 other at the point of contact by the original wall of the con- 

 jugating suspenders. This division soon becomes perforated, 

 and at length disappears, leaving the twin discoid cells united 

 into a subglobose central cell, which is to become the zygospore. 

 The membrane thickens, becomes warted and of a dark colour, 

 nearly black, when it reaches maturity, and in this condition 

 it settles to a period of rest. 



In the family of Sa'prolegniaccdc the oogonia, or female 

 cells, are terminal on short branches of the mycelium (Fig. 37). 

 They are globose cells, the membrane 

 of which is soon perforated, and at the 

 same time the contents are differentiated 

 into rounded little spheres which float 

 in the interior. From the pedicel of 

 the oogonia, or from neighbouring 

 hyphae, short curved branches arise, 

 which bend towards the oogonia. These 

 are the antheridia, which become slightly 

 swollen at the apex, and closely applied 

 to the wall of the oogonium. About 

 the time when the gonospheres are 

 formed each autheridium projects into 

 the cavity of the oogonium one or more slender tubes, 

 but these appear never to open or discharge their contents, 

 so that they cannot fertilise the gonospheres, which, however, 

 soon acquire a cellulose membrane, and the process is complete. 

 This is the general character of the sexual reproduction, 

 modified somewhat according to the genera and species. 



Another family, the Peronosporaceae, possesses an asexual 

 system of reproduction much resembling that of ordinary 

 Mucedines, but parasitic on living plants. The mycelium, 

 which permeates the tissues, usually in the autumn produces 

 oogonia, which arise from swellings of the mycelial tubes. 

 These take the form of globose cells, which become divided off 

 at the base by a septum (Fig. 3 8). Other branches swell at the 



Fig. 37. — Oogonium with 

 two oospheres of Achlya. 

 After De Bary. 



