1905.] Development of the Ascocarp q/*Humaria granulata. 



359 



surrounding cells which leads to a slight collapse of the wall, and so to the 

 obliteration of the cavity of the ascogenous hyphae at their point of origin. 

 Ultimately the whole ascogonium becomes obliterated, though it remains con- 

 spicuous as a large empty vesicle up to the time when the ascocarp first opens 

 (fig. 81). The stalk cells also become emptied (fig. 30), and are obliterated 

 somewhat earlier, so that after the early stages of opening no trace at all of 

 the archicarp can be observed. It may be mentioned here that the nuclei 

 of the uppermost stalk cell are generally more distinct than those of the 

 ordinary vegetative hyphae, being intermediate in structure between those 

 and the ascogonial nuclei (figs. 11 and 12). 



In the earlier stages of development the whole of the nourishment for the 

 growth of the apothecium is supplied by the archicarp from its reserve of 

 material, the cells of the stalk supplying the branches which arise upon them, 

 while the ascogonium supplies the ascogenous hyphae. In the later stages, 

 however, a " secondary mycelium " is formed consisting of vegetative hyphse 

 which grow down into the substratum and absorb nourishment which is 

 -supplied to the vegetative hyphae of the ascocarp, and so indirectly to the 

 ascogenous hyphae which, after the emptying of the ascogonium, are practically 

 parasitic on the vegetative hyphae. 



The first asci are formed very early before the outer peridium is burst 

 through (fig. 30) ; they arise on the ends of the ascogenous hyphae by the 

 peculiar process of the bending over of the apex and the fusion of the nuclei 

 in the sub-terminal cell (figs. 20 to 25), such as has been described by Harper, 

 Dangeard, Guillermond, and Claussen. In two cases the ascus was observed 

 in a terminal position as described by Maire(23) and by Guillermond (14) 

 for Galactinia succosa. 



When the two nuclei have fused in the ascus, the fusion nucleus begins to 

 increase in size and to show a definite chromatin substance between nucleolus 

 and wall. 



The division of the nucleus does not call for any particular comment, as it 

 is not very favourable for investigation ; the spindles are at first intranuclear 

 and show well-marked centrosomes with radiations, but the chromosomes are 

 too small to allow of an estimation of their number (figs. 26 to 28). 



The method of spore formation in the ascus appears to be of the well-known 

 type first described by Harper, but owing to the density of the contents of 

 the ascus and the somewhat small size of the spores the object is not a 

 favourable one for the study of the details of the process (fig. 29). 



The paraphyses at their first appearance form a wedge-shaped mass, which 

 appears to play a part in bursting open the peridium, as described by Harper 

 in Ascobolus. 



VOL. LXXVII. — B. 2 D 



