360 BOTANY 



the reticulately indented exterior surface (Fig. 273, p. 351). The Morchellas are 

 edible, and have an agreeable taste and smell, in particular M. esculenta and M. 

 conica. Helvella esculenta, which is also edible, has a whitish stalk and a dark- 

 brown pileus ; but Hdvella suspecta, with a reddish-brown pileus and a dirty 

 flesh-coloured stalk, has a nauseous sweetish taste, and is regarded with suspicion. 

 Verpa digitaliformis, which has a long-stalked, bell-shaped pileus, is also edible. 

 In their external appearance the fructifications of these highly-developed Disco- 

 mycetes greatly resemble those of the Basidiomycetes. 



In the Helvellaceae the production of conidia as an accessory form of fructification 

 is not known to occur, but in the other Discomycetes the formation of conidia fre- 

 quently takes place in the same manner as in the Pyrenomycetes. 



Sub-Class 5. Hemibasidii 



Just as the Hemiasci occupy an intermediate position between the 

 sporangiferous Zygomycetes and the Ascomycetes, the Hemibasidii connect 

 the conidia-bearing Zygomycetes and the Basidiomycetes. Their conidio- 

 phores bear a close resemblance to the basidia of the Basidiomycetes, 

 but differ from the latter in producing spores less definite in form 

 and number. Both the Hemibasidii and the succeeding sub-class, Basi- 

 diomycetes, are highly organised Fungi with septate mycelia. They 

 are devoid of any sexual mode of reproduction ; the asexual formation 

 of spores is never effected in sporangia or asci. 



The Hemibasidii comprise but one order, the Brand Fungi. They 

 are parasites, and their mycelium is found ramifying in higher plants, 

 usually in definite organs, either in the leaves and stems, or in 

 the fruit or stamens. The Gramineae in particular serve as host- 

 plants for the Brand Fungi, certain species of which are in a high 

 degree injurious to cereals, and produce in the inflorescences of Oats, 

 Barley, Wheat, Millet, and Maize the disease known as smut. 



At the end of its period of vegetation the, mycelium of the 

 Brand Fungi produces in or upon the host-plant the so-called brand 

 spores by the formation of additional transverse walls, and by the 

 division of its profusely branched hyphse into short swollen cells 

 (Fig. 284, A). The cells become rounded off and converted into 

 spores, while their cell walls undergo a mucilaginous modification. 

 The spores thus surrounded by gelatinous envelopes, which, how- 

 ever, eventually disappear, then become invested with a new, thick, 

 double wall, consisting of a thin colourless endosporium and a 

 thick dark - coloured exosporium. In this way- the mycelium is 

 transformed into a dark - brown or black mass of spores. As 

 regards the manner of their formation, the brand spores may be 

 regarded as chlamydospores, similar to those formed in the case of the 

 Hemiasci by Protomyces (Fig. 272, p. 350), and occurring also in 

 certain of the Zygomycetes and in many of the higher Fungi. In the 

 formation of chlamydospores by the septation of the hyphee, an 

 essentially different mode of spore-formation is exhibited than that 



