INJURIES INDUCED BY PLANTS 69 



ASCOMYCETES. SAC FUNGI 



This second group of fungi has obtained its name through the 

 spores being produced in the interior of sacs (asci). In some 

 cases the sporocarp results from a sexual process.* The fungi 

 belonging to this group are very numerous, and are arranged 

 in four orders the Erysiphece^ Tuberacece^ Pyrenomycetes, and 

 D is corny cetes. 



THE MILDEW FUNGI, ERYSIPHEJE 



All the mildew fungi are true parasites. Their mycelium 

 vegetates on the surface of plants that is to say, on the 

 epidermis of leaves, fruits, and stems, and obtains its nourishment 

 by means of haustoria from the interior of the epidermal cells, 

 which consequently turn brown and die. The ascocarps which 

 are developed on the mycelium are usually globular and com- 

 pletely closed that is to say, unprovided with an apical or other 

 opening,-)- and may be recognized with the naked eye as small 

 dark specks. These hibernate and carry the fungus over to the 

 following year, while in the course of the summer gonidia are 

 formed by abscission on numerous simple erect hyphse. These 

 are at once capable of germinating, and spread the disease during 

 the period of growth. On account of the interwoven mycelia and 

 gonidiophores, when luxuriantly developed, forming a fine grey 

 meal-like covering on the upper surface of the leaf, the term 

 " Mildew" has been applied to the disease. 



As a preventive measure, the burning in autumn of leaves 

 infested by the cleistocarps of the fungus has been recommended, 

 while sprinkling sulphur on the diseased parts after the mildew 

 has appeared in summer is said to be efficacious. Unfortunately 

 no scientific investigations regarding the action of the powdered 

 sulphur on the mycelium of the fungus have as yet been 

 undertaken. 



*[The Sporocarp (in this case termed an Ascocarp) is often a very com- 

 plex body. The question as to its origin and morphological nature cannot 

 be discussed here, and the reader is referred to the special works of De Bary, 

 Brefeld, &c., already quoted. ED.] 



t [These closed Ascocarps are termed Cleistocarps, in distinction from 

 the perforated Perithecia of the Pyrenomycetes and the open Apothecia of 

 the Discomycetes. ED.] 



