ASCOMYCETES 



27 



inches below the surface of the ground. They are much esteemed as an article 

 of diet when in season (March — June)*. 



The fungus causing the mildew of the vine is known botanically as 

 Uncinula spiralis]'. The mycelium of the fungus, unlike that of Phytophthora 

 and most other parasites, does not penetrate the tissues of the host-plant, 

 but forms a web on the outside only, attached to the leaf or berry by 

 means of very minute outgrowths from the hyphae called haustovia, 

 which penetrate the outer cells and extract nourishment from them. Here 

 and there, on the mycelium, short upright hyphae occur, on which chains 

 of conidia develop (Fig. 20 A), each conidium being capable of immediate 

 germination if carried by the wind to another leaf. It is the presence of 

 these conidia which gives the characteristic appearance of a " mildewed " leaf, 

 as though flour had been dusted on the surface. In South Africa no other 

 method of reproduction is met with, but in North America the ascus-bearing 

 fruit-body (cleistocarp) is sometimes found (Fig. 20 C). This is nearly 



spherical and consists of a somewhat thick 

 wall, bearing a number of long, simple hairs 

 coiled near the apex, and enclosing a small 

 number of oval asci, each containing four or 

 eight ascospores. The cleistocarp, owing 

 to its thick hard wall, can withstand long 

 periods of drought. 



Sub-class B. Pyrenomycetes. A good 

 South African representative of this order 

 is a fungus, parasitic on yellow-wood trees 

 (Podocarpus), called Corynelia (see Fig. 21, 

 also Plate 17, Fig. A, 4). In the same 

 figure is illustrated another very closely re- 

 lated fungus, also occurring on Podocarpus at 

 the Cape, and only differing in the shape of 

 the spores. The perithecia are about a 

 millimetre in length as shown in Fig. 21, 1. 

 Fig. 21, 9 represents a section of one of 

 the perithecia. From the base of this are 

 borne a considerable number of asci (2), each 

 with eight brown spores. Other smaller 

 flask-shaped cavities are also met with, called 

 pycnidia (4), each lined with hyphae 

 bearing exceedingly small pycnospores 

 (5). Some trees in damp situations suffer 

 considerably from the attacks of this fungus. 



The " Ergot " of grasses, especially of the rye, also belongs to this order. 



* Terfezia Claveryi and T. Boudieri, both known from North Africa and used there 

 under the name "terfaz." 



f The "true mildew" of the vine, more generally known as Otdtum Tuckeri; but 

 this name applies only to the conidial stage. 



4—2 



Fig. 20. Uncinula necator ( U. spi- 

 ralis). A. Conidiophores, 

 c, conidia. B. Mycelium on 

 surface of leaf of vine. /;, haus- 

 torium. C. Cleistocarp (peri- 

 thecium). (After Sorauer and 

 Lindau, Pflanzenkrankheiten) 



