HELIOTROPISM OF ASCI IN DISCOMYCETES 275 



grow in all directions so that a ball of interwoven hyphae with the 

 ascogonium near the centre results (c). Then tissue differentiation 

 begins {d). The cells of the outer layers enlarge and often become 

 thick-walled, forming a pseudoparenchymatous cortex, while the 

 internal hyphae remain thin-walled, and continue to branch, so that 

 the spaces which would be formed by the expansion of the cortex 

 are filled. A mucilage cavity then forms in the upper part of the 

 spherical mass internal to the cortex (e). It originates partly by 

 the stretching of the internal tissue but mainly by the dissolution 

 of the internal hyphae. Numerous hyphae grow into the cavity as 

 a palisade layer which spreads from the floor over the sides to the 

 roof. Some hyphae are outgrowths from cells lining the cavity, but 

 others are said to originate from the neighbourhood of the 

 ascogonium and to grow up with the ascogenous hyphae. The 

 ascogenous hyphae are produced from the ascogonium after its 

 envelopment and on reaching the floor of the cavity begin to form 

 asci. The upgrowth of the palisade hyphae is soon arrested 

 and they are transformed into paraphyses, which act marks the 

 beginning of the hymenium (/). 



" Subsequently the cortical layer overlying the mucilage cavity 

 is ruptured by the expanding internal tissue, and about the same 

 time the first asci are formed {g). The intercalary grow^th of the 

 hymenium, due to the production of asci and paraphyses, presses 

 the sides of the apothecium apart, exposing the disc (g), while the 

 apothecium passes through a characteristic turbinate shape before 

 becoming lenticular. 



" Finally, in stage (h), a marginal growing-point is formed, and 

 apparently from the hyphae which grew from the sides of the 

 mucilage cavity and which, on exposure of the disc, form a 

 sympodium : the outer laterals are converted into cortical hyphae 

 and the inner ones into paraphyses. 



" Evidently primary and secondary parts can be distinguished 

 in the angiocarpic apothecium. The primary part consists of the 

 archicarp, the investing hyphae, and the initial part of the 

 hymenium, and the primary period of development comprises all 

 stages up to (g) (Fig. 131). The secondary part consists of all 

 tissues derived from the marginal growing-point, and the secondary 



