OBSERVATIONS ON THE GENUS PYTHIUM. 491 



of sexual organs, and of the sexual act to be followed on one 

 specimen.^ I will describe the different phases as observed on 

 such a cultivated example. 



From a branch which had developed into the surrounding 

 water, an apical swelling was formed exactly as for a ternnnal 

 conidium: much dense granular protoplasm accumulated in 

 this, and then a septum formed below. Soon afterwards, 

 a lateral protuberance arose from the hypha immediately 

 below the septum ; this rapidly developed as a somewhat club- 

 shaped branchlet, also filled with protoplasm, which curved 

 upwards towards the large spherical terminal body. The first 

 formed, conidium-like sphere is the oogonium; the smaller, 

 clavate body, the antheridium. In the case described — a 

 very common one in this species — the antheridium, having 

 become separated by a septum from the common parent hypha, 

 pushed aside the oogonium as its apex came in contact 

 with it (fig. 9). The antheridium does not, however, al- 

 ways arise immediately beneath the oogonium ; it may even 

 spring from a different branchlet (fig. 8), and other cases 

 occur. 



On an oogonium favourably situated for examination I 

 made the observations illustrated at fig. 10. This specimen was 

 continuously watched from a little before eight o'clock in the 

 morning till three o'clock in the afternoon, drawings being 

 made at intervals, when the progress of events was marked by 

 changes of special interest or importance. 



At 8.15 a.m. the oogonium and antheridium had been 

 completely formed, and in contact for some time, the apex of 

 the latter being closely attached to the oogonium wall, and 

 having already commenced to send a short process into it. The 

 contents of the antheridium were bright and less dense than 

 those of the oogonium, with several large brilliant granules 

 scattered inside; a firm septum marked off" this upper part 

 of the antheridium from the rest. At a period just preceding 



1 In many cases the mycelium grows down, across the cavity of the damp 

 chamber, and, carrying water with it, spreads on the glass slip below : excel- 

 lent preparations of the sexual organs in all stages may thus be obtained. 



