76 DIVISION I, GENERAL MORPHOLOGY. 



SECTION XIX. b. The asci (thecae) are in almost all cases the solitary 

 terminations of hyphal branches; several or many of these asci, in most cases 

 a very large number of them, arranged nearly parallel to one another and with hairs 

 (paraphyses, section XII) between them are grouped together to form hymenia, which 

 in the Discomycetes are open superficial layers on the sporophores, but in the Pyreno- 

 mycetes are in the interior of receptacles (perithecia) which are either closed or 

 provided with a narrow orifice. See sections LIX LXII, where some account is 

 given of the exceptions to the rule thus briefly stated. 



The formation of the asci is not essentially different from that of other terminal 

 cells of hyphal branches. They are generally club-shaped, more rarely broadly 

 ellipsoid or are stalked spheres as in Tuber, Elaphomyces, Erysiphe, Eurotium, and 

 others ; and when once orientated they grow on usually without interruption till they 

 attain their definitive shape and size and then in most cases begin immediately to 

 form spores. It is only in some species of Erysiphe that the formation of spores 

 is preceded by a longer period of rest ; it is indeed possible that young immature 

 asci may pass through the winter period of rest in the case of species which, like 

 Rhytisma and its allies, form their spores in spring, but this has never been directly 

 observed. 



In the very large majority of cases eight primordia of spores are formed simultane- 

 ously in each ascusj the facts connected with this proceeding were carefully 

 investigated by myself in 1863 J in certain species of Peziza, Helvella, and Morchella, 

 by Strasburger 2 recently in Anaptychia ciliaris, and by Fr. Schmitz z in species of the 

 same genera and of Ascobolus, Chaetomium and Exoascus, with the following results. 



In a number of Pezizas (P. confluens, P., Fig. 39, P. pitya, P.) the young ascus is 

 rilled with finely granular protoplasm containing vacuoles ; a nucleus may be seen in 

 the centre of the protoplasm, as soon as the tube has reached about a third of its 

 ultimate length, in the form of a clear spherical body, in the centre of which is another 

 smaller and strongly refringent body. It has yet to be learnt whether the whole 

 body should be called the nucleus and the inner and smaller body the nucleolus, or 

 whether the latter alone is the true cell-nucleus. 



As the ascus elongates the protoplasm moves into its upper extremity, and the lower 

 portion, which may constitute three-fourths of the whole length^ now contains only a 

 more watery fluid and a thinner parietal layer of protoplasm. When the ascus has 

 reached its full length, the commencement of spore-formation is indicated by the 

 appearance of two smaller nuclei in the place of the original nucleus. In a later stage 

 four nuclei are seen and then eight ; the nuclei are always of similar structure but 

 their size diminishes as their number increases. Their arrangement and Strasburger's 

 observations on Anaptychia leave no doubt that they are produced by successive 

 bipartitions from the primary nucleus. The eight nuclei of the last order are about 

 equidistant from one another, and are each ultimately surrounded by a sphere of 

 protoplasm, which is distinguished from the rest of the protoplasm by its greater 

 transparency and has a very delicate line of delimitation. These portions of protoplasm 



Die Fruchtentwickelung d. Ascomyceten, p. 34. 



Bot. Ztg. 1872, p. 272. Zellbildung u. Zelltheilung, Aufl. 3, p. 49. 



See above on page 16. 



