242 ERGOT (CLAVICEPS) 



more central ones, forming the lighter-coloured region, are laden 

 with food-reserves. The sclerotia drop off in the autumn and 

 remain dormant in the soil until the following spring. Then 

 they send up one or more stalked swellings (Fig. 128, D), in 

 which are embedded numerous flask-shaped cavities (perithecia, 

 Fig. 128, E, p.) communicating with the exterior by small pores 

 (Fig. 128, F). Each perithecium is lined with a hymenium 

 similar to that of Peziza, but the ascospores developed within 

 the asci are in this case thread-like (Fig. 128, G), so that they 

 are readily distributed by the wind. If caught by the stigma 

 of a Grass-flower the spores germinate and the hypha grows 

 down through the style into the ovary, thus bringing about a 

 fresh infection. 



By slow degrees the contents of the ovary are replaced by a 

 dense hyphal mass with deep surface furrows (Fig. 128, B, upper 

 part). From the ends of the superficial hyphae, which are more or 

 less parallel to one another, large numbers of minute oval gonidia 

 are budded off (Fig. 128, C), and at the same time the surface 

 secretes a sugary liquid. This attracts insects, to whose bodies the 

 gonidia adhere, and so a rapid spread of the disease from flower 

 to flower is brought about. Later in the summer the production 

 of gonidia ceases and the outer hyphae blacken, whereby the 

 resting sclerotium is formed. 



The bright red pustules of Nectria and the branched sclerotia 

 of the Stag's Horn Fungus (Fig. 126, A) harbour flask-shaped 

 perithecia similar to those of the Ergot. 



In some Ascomycetes reproduction by gonidia is far more 

 frequent than the formation of asci, as, for instance, in the two 

 common Moulds Penicillium (Fig. 129, a, b) and Eurotium 

 (Aspergillus, Fig. 129, /). Here the gonidia are budded off in 

 chains from the terminal branchlets of erect hyphae which, in 

 the case of Eurotium (Fig. 129, /), are strongly swollen at their 

 apices. Both Fungi also occasionally produce spherical ascus- 

 fruits (Fig. 129, d), which arise from special sexual organs 

 (Fig. 129, c), although it is doubtful whether any actual fusion 

 of cell-contents occurs. 



In the White Mildews (Erysiphacece) 1 formation of gonidia 



1 The Mildews are the cause of many familiar diseases of cultivated 

 plants, as instances of which may be mentioned the Gooseberry Mildew 



