iv] PEZIZALES 123 



The apothecia of the majority of forms included in these two families 

 are small, often stalked, sometimes attached to a sclerotium ; they are waxy 

 in consistency and may be glabrous or hairy. Must are saprophytes, often 

 occurring on dead plants, some are parasitic. In Helotiaceae they are 

 almost always sunk in the substratum (immersed), and in Mollisiaceae 

 frequently superficial. 



Among the Mollisiaceae Pseudopezisa Trifolii is parasitic and causes the 

 leaf-spot disease of clover. The leaves become increasingly spotted and 

 die, so that the crop is often seriously injured. In this case the ascocarps 

 are sessile and distinctly erumpent, developing within the tissue of the leaf, 

 and breaking through the epidermis at maturity. There are several other 

 species of Pseudopeziza, most on dead stems and leaves, a few on the living 

 tissues of wild plants. The species of Tapesia occur on wood, branches, 

 and dead leaves. The ascocarps are stipitate and pilose or downy, they are 

 found in groups seated on a spreading weft of branched interwoven hyphae, 

 by means of which the genus is readily distinguished. T. fusca is to be 

 found on fallen twigs of larch and other plants. 



Among the Heliotiaceae the genus Helotium includes a number of species 

 found on dead leaves, stems, beechmast, and similar habitats; these fungi 

 are light-coloured, waxy and frequently stipitate. 



Another large genus, Dasyscypha, has a sessile or short-stalked ascocarp, 

 thin and delicate in texture, and externally pilose; the species are sapro- 

 phytic or parasitic. Dasyscypha Willkommii is the cause of a serious 

 disease, the well-known Larch Canker. The apothecia are externally yellow 

 with an orange disc. The ascospores give rise to germ-tubes which are 

 unable to penetrate the bark, but obtain entrance through wounds caused 

 by hail, ice or snow, or by the destruction of the needles by insects. The 

 Larch moth (Coleophora laxicelld), for instance, is known to cause less injury 

 in mountainous than in lower regions, and the fungal disease is propor- 

 tionately less prevalent in the mountains. The mycelium ramifies chiefly 

 through the soft bast, but may penetrate the wood as far as the pith. It 

 spreads only in the autumn and winter, never in summer when the growth 

 of the host is active. Where it spreads into the bark the tissues turn 

 brown and shrivel, causing depressed canker spots in which yellowish white 

 stromata are produced. These give rise to minute unicellular conidia, and 

 later, if the atmosphere is sufficiently moist, to ascocarps. 



In the genus Sclerotinia the stalked ascocarps arise from sclerotia (fig. 81 i I. 

 A number of species arc parasitic : S. tuberosa on - Xnemone nodosa; S. sclero- 

 tiorum on the potato, cabbage and other hosts in the stems of which the 

 sclerotia are formed; S.fructigena and .V. entered on species of Prunus and 

 Pyrus where they give rise to brown rot, blossom wilt and other pathological 

 conditions; ,s'. bulborum on hyacinth and other bulbs, and various species on 



