44 



FUNGI. 



through all the genera to illustrate this chief feature of coloured, 

 septate, rather rigid, and mostly erect threads, bearing at some 



point spores, which in most in- 

 stances are elongated, coloured, 

 and septate. 



Mucedines. — Here, on the other 

 hand, the threads, if coloured at 

 all, are still delicate, more flexuous, 

 with much thinner walls, and never 

 invested with an external cortical 

 layer. One of the most important 

 and highly developed genera is 

 Peronospora, the members of which 

 Fig. 26.—Acrothecium simplex. are parasitic upon and destructive 

 of living vegetables. It is to this genus that the mould of the 

 too famous potato disease belongs. Professor De Bary has done 

 more than any other mycologist in the investigation and eluci- 

 dation of this genus ; and his mono- 

 graph is a masterpiece in its way.* 

 He was, however, preceded by Mr. 

 Berkeley, and more especially by Dr. 

 Montagne, by many years in eluci- 

 dation of the structure of the flocci 

 and conidia in a number of species.f 

 In this genus, there is a delicate 

 mycelium, which penetrates the in- 

 tercellular passages of living plants, 

 giving rise to erect branched 

 threads, which bear at the tips of 

 their ultimate ramuli, sub-globose, 

 ovate, or elliptic spores, or, as De 

 Deeply seated on the mycelium, 

 within the substance of the foster plant, other reproductive 

 bodies, called oogonia, originate. These are spherical, more or 



* De Bary, " Champignons Parasites," in "Ann. des Sci. Nat." 4 me ser. vol. xx. 

 t Berkeley, "On the Potato Murrain," in " Journ. of Ilort. Soc. of London," 

 vol. i. (1846), p. 9. 



Fig. 27. — Peronospora Arenarice. 



Bary terms them — conidia, 



