INJURIES INDUCED BY PLANTS 131 



previous year may also die back for a certain distance 

 (Fig. 71). 



One afterwards observes, both on the leaves and on the 

 twigs, small black sclerotia not larger than a pin-head. In 

 a moist chamber these germinate and produce the gonidiophores 

 of Botrytis. The gonidia germinate easily, and infect the tender 

 shoot of the Douglas fir. Tubeuf s researches show that silver 

 firs, spruces, and larches were also infected by this fungus, 

 and it remains to be determined whether diseases in the forest 

 may not also be induced by it. 



GYMNOASCE.E 1 



In the case of the parasites that belong to this sub-family 

 of the Discomy cites y there is no proper fructification. The 

 hymenium is a flat layer which occupies the surface of the 

 plant, and consists of free tubes which develop among the 

 epidermal cells, or between the epidermis and cuticle. 



All the species induce characteristic hypertrophy of the 

 part of the plant that is attacked. 



EXOASCUS PRUNI 2 * 



This is a widely distributed parasite, which is familiar enough 

 by causing the formation of the so-called " Mock," " Pocket," 

 " Starved," &c., plums. Its mycelium persists from year to 

 year in the soft bast of the branches of Primus domestica, 

 P. spinosa, and P. Padus, in which it grows intercellularly, 

 gaining access to and contorting the young leafy shoots. The 

 same is true in the case of the flowers, where malformation of 

 the ovary is recognisable even in the beginning of May. 

 Proceeding from the soft bast the mycelium spreads through 

 the fleshy parenchyma of the fruit, where, on the one hand, 

 it prevents the formation of the stone and seed, and, on the 

 other, induces elongation and the well-known deformation of the 



1 Sadebeck, Untersuchungen ilber die Pilzgattung " Exoascus" Hamburg, 

 1884.* 



2 De Bary, Beitrdge zur Morphologic der Pilze, I. p. 33. 



* [Common in this country. Sadebeck has just published an exhaustive 

 monograph on the whole group of parasitic Exoascece (Hamburg, 1893), 

 revising the classification, and clearing up many doubtful points. ED.] 



K 2 



