ON SAPROiiEGNi^. 273 



rhizoid-like branches penetrating the tissues from which the 

 fungus radiates. 



De Bary has lately pointed out that the " intramatrical^ 

 portion of the thallus does not spread far in the tissues^ and no 

 extension of the fungus occurs by outward developments from 

 its internal branches; the hyphse outside, however, continually 

 send downward prolongations, which take root and spread 

 slightly in the attacked tissues, and thus the area of " intra- 

 matrical" hyphse becomes extended. ^ Hence, if zoospores, &c., 

 are prevented from again attacking the matrix from without, 

 the Saprolegnia thallus does not extend far within the tissues 

 — an important distinction between these fungi and those which, 

 like Pythium, &c., attack a host at one point and send rami- 

 fications in all directions inside the tissues. The difference is, 

 roughly speaking, analogous to that between a banyan tree and 

 a bamboo, in so far that the former extends its area of feeding 

 ground by sending down prolongations from its outer branches 

 to root afresh in the matrix or earth, while the latter extends 

 itself under the surface by means of underground shoots, which 

 protrude here and there further from the parent stock. 



The tubular hyphae forming the thallus vary much in 

 diameter, partly according to position, main stems and branches 

 being thicker than secondary and tertiary ones; their cellulose 

 walls are very thin and transparent, and enclose protoplasmic 

 and oily contents. These latter are, as a rule, very coarsely 

 granular, causing the thallus branches to appear dense and 

 opaque, usually with a yellowish hue. 



Septa occur very rarely in the tubular branches, but are 

 always found separating the zoosporangia and the sexual re- 

 productive organs from the purely vegetative portions of the 

 thallus. 



The Saprolegnise have usually been stated to be a-nucleate 

 in common with other fungi." This, however, is not the case ; 



publication is now the most important authority for the morphology of the 

 group. 



' Loo. cit., pp. 95 to 97. 



2 Luerssen, 'Med. Pharm. Bot.V1879, B. 1, p. 72, and Sack's 'Lehr- 

 buch,' 17 ed. 



