Hick: The Sexual Eepeoduotion of Fungi. 99 



which are developed in the clavate extremities of the threads, and it is 

 only after an indefinite number of such generations have been produced, 

 that the sexual individuals make their appearance. 



The free ends of certain threads swell up into a globular form and 

 become filled with a dense and richly granular protoplasm. The cavity 

 of this globular body becomes separated from that of the filament by a 

 transverse wall, and it then forms the Oogonium. The protoplasmic 

 contents of the Oogonium contract by the expulsion of water and divide 

 into two, four, or more portions, which rounding themselves off consti- 

 tute the oospheres, and await the advent of the male element. 



Meanwhile the male organs are also formed as much thinner lateral 

 branches which usually arise below the Oogonium. They are as a rule 

 strongly curved so that their extremities are brought into close proximity 

 with the Oogonium. The extremity of each branch swells a little and 

 becomes separated by a transverse wall, giving rise to a large terminal 

 cell, which is the Antheridium (Fig. 3). 



The process of fertilization of the oospheres by the contents of the 

 Antheridium appears to be a remarkable one. According to Pringsheim 

 the inner wall of the Oogonium produces at different points a number of 

 wart-like knobs, which may or may not remain covered with the outer 

 wall. When the Antheridium is fully formed it applies itself firmly to 

 the outer wall of the Oogonium, and manages to cover one or more of the 

 points at which warty protuberances have arisen. The inner wall of the 

 Antheridium now develops a small protuberance which penetrates the 

 Oogonium wall, comes in contact with one of the projections from the 

 inner layer, through which it grows, forming a short narrow tube whose 

 extremity conceals itself among the oospheres. The end of the fertilizing 

 tube now opens itself ; the contents of the Antheridium pass through 

 into the Oogonium, and the oospheres become fertilized thereby. Subse- 

 quently they surround themselves with thick firm walls, and remain for 

 months quietly lying in the Oogonia. When germination takes place 

 the oospore either develops a germ tube, which immediately grows to a 

 branched plant, in which later on zoospores are found, or the oospore 

 puts forth a sLort tube which opens at the apex and empties the whole 

 of its contents in the form of zoospores. 



Pero7iospore(B. The type of this order, Feronospora infestans^ has been 

 the subject of repeated observation and discussion owing to the fact that 

 it is the chief cause of the well-known potato disease. Very prolonged 

 investigations into its hife-history have been made by Mr. Worthing- 

 ton G. Smith whose papers in the Gardeners' Chronicle, Monthly 

 Microscopical Journal, and Quarterly Journal of Microscopical Science 



