88 FUNGOID PESTS OF CULTIVATED PLANTS. 



GARDEN PEA RUST. 

 Uromyces Pisi (Pers.), PI. VII. fig. 110. 



The Pea rust is not so common as the "Pea mildew ",on garden Peas, 

 but it is developed in the tissues, and at length makes its appearance 

 externally by bursting in little pustules through the cuticle of the leaves. 



The earlier pustules are brown, of a paler colour than the later ones, 

 powdery, and of a rust colour. These uredospores are rather globose, or 

 a little elongated, with a roughened or minutely spiny surface (17 x 24). 



The teleutospores are produced in similar pustules, but are darker, 

 and of a brownish-black in the mass. They are broadly elliptical, with a 

 suggestion of pear-shape, being narrowed downwards into a long and 

 colourless pedicel (20-32 x 17-21 p) ; the apex of the spore has the 

 coat, or tegument, a little thickened, and the whole surface is delicately 

 punctate when fresh, but apparently quite smooth when old or dried. 

 The uredospores are much more common on the garden Pea than the 

 teleutospores, which latter are comparatively rare. 



Those who believe in heteroecisrn affirm that the cluster-cups of this 

 rust are produced upon the leaves oi' the Wood Spurge (Euphorbia 

 Cyparissias). 



This rust occurs in France, Belgium, Germany, Austria, Bohemia, 

 Switzerland, Finland, Italy, Sicily, and Siberia. 



Sacc. Syll. vii. 1941 ; Cooke, M. F. p. 212 ; Tubeuf, Dis. 834 ; Plowr. 

 Brit. Ured. 133. 



PEA MILDEW. 

 Erysiphe Martii (Lev.), PI. VII. fig. 111. 



Everyone with a garden knows the "Pea mildew" too well, the 

 whitened leaves, covered on both sides, as if with hoar frost or a thin 

 coating of whitewash, showing the sickening yellowish leaves beneath. 

 "This mildew is very common, es^cially towards the close of the season, 

 destroying the last crop. Seen by the naked eye the white coating is 

 soon sprinkled with minute black dots which are the receptacles of the 

 final stage. 



The white coating consists of a rather dense mycelium of interwoven 

 threads so compact as to choke up the stomates of the leaves. Here and 

 there, scattered over the mycelium and projecting from it, are little 

 suckers, or haustoria, which enable the mycelium to retain its hold. At 

 first the threads of the mycelium, which arise as fertile branches, only 

 produce conidia, in chains, of the kind known as Oidium. Afterwards the 

 black dots appear, which are at first orange, then brown, and finally 

 black, seated upon and scattered over the mycelium. These are the 

 receptacles, which, when magnified, are seen to be globose bodies, held 

 down by little root-like filaments at the base, while a circle of flexuous 

 threads are disposed about the lower circumference. These receptacles 

 contain the mature fruits of the parasite, which are small colourless, 

 nearly elliptical sporidia, enclosed in transparent sacs or asci, of a some- 

 what pear- shape. Each receptacle holds from 4 to 8 of these asci, each 

 of which encloses from 4 to 8 sporidia. When quite ripe thd receptacles 

 are split open and the sporidia escape, and perpetuate the species. 



