10 THE SAPROLEGNIACEAE 



observation for a period of five months it has been found possible 

 to obtain on the same mycelium the methods of asexual reproduction 

 which are characteristic of six different genera." If this claim is ex- 

 amined it will be seen that outside of its own genus {Saprolegnia) the 

 species he describes cannot with accuracy be said to show the methods 

 of asexual reproduction of any other genera except Aplanes and Lepto- 

 legnia, and even in these cases only in certain details, not in all. The 

 sporangial variations cited do not look like the sporangia of the genera 

 in question and neither do the spores within them, and no one familiar 

 with these genera would be misled into placing them there unless one's 

 attention be focused on the wording of keys rather than on the plants 

 themselves. Such variations as these do not, as Lechmere implies, create 

 doubt of the validity of the presently accepted classification of the 

 Saprolegniaceae. 



The egg structure falls into two main types. In all cases the fatty 

 reserve is on or near the periphery, but in one type it is in the form 

 of small droplets entirely surrounding the protoplasm, while in the other 

 it is collected into one or a few larger drops on one side. The first of these 

 types is called centric, the second eccentric, but intergrading types occur 

 which connect the two extremes, and for certain of these I have found it 

 useful to introduce the word subcentric. The three terms may be de- 

 fined as follows: 



A centric egg has one or two layers of small fat droplets entirely 

 surrounding the central protoplasm. 



A subcentric egg has the protoplasm surrounded by one layer of 

 droplets on one side and two or three layers on the other, or rarely with 

 the droplets entirely lacking on part of one side as in Achlya oblongata; 

 this last condition connecting directly with such eccentric structure as 

 is shown by Pythiopsis cymosa. 



An eccentric egg has one large drop on one side either outside the 

 protoplasmic surface or barely enclosed by a thin layer of protoplasm, 

 or several large drops enclosed in the protoplasm on one side, or a lunate 

 row of small drops (in optical sections) on one side, as in Pythiopsis cymosa. 



The egg structure is of much systematic significance. It is always the 

 same in a given species and is often the same throughout an accepted 

 genus, or else in groups of obviously related species within a genus. 



Since Humphrey's review of the cytology of spore formation there 

 is nothing of importance to add, except the work by Rothert referred to 

 above and the careful study by Weston of the exact shape of the spores 

 in Achlya ('17), Thraustotheca ('18) and Dictyuchus ('19). The cytology 



