266 DIVISION II. COURSE OF DEVELOPMENT OF FUNGI. 



(E. aureus). In the latter case especially and in the last-named species the outer 

 extremity of each ascus bursts through the cuticle, while the inner extremity grows into 

 a narrowly conical process, which becomes deeply and firmly fixed between the lateral 

 walls of the epidermal cells. The forms of a third series, represented by Sadebeck's 

 Exoascus epiphyllus, which grows on Alnus incana, and E. Ulmi, also spread their 

 hyphae between the cuticle and the wall of the epidermal cells, but form their asci 

 from a part only of their cells, while the other part remains sterile ; hence the asci are 

 here less crowded. 



The structure of the asci, the formation of the spores in them, and the ejection of 

 the spores by mechanical contrivance, are essentially the same, as far as is at present 

 known, as in other organs of the same name. The number of the simultaneously 

 formed ascospores is also usually eight in Exoascus Pruni ; other numbers will be 

 mentioned further on. All the spores are small, simple, ellipsoidal cells with a delicate 

 colourless membrane. 



The spores of Exoascus Pruni are ejected when ripe and germinate at once in 

 water or a nutrient solution, sprouting repeatedly and perfectly and forming many 

 orders of sprouts. Those of the first orders are of much the same shape and size as 

 the mother-spore, those of the higher are often much smaller. If the ripe spores 

 are detained in the ascus, they often form their germ-sprouts in it, and the ascus 

 becomes filled with countless sprouts of different orders and sizes, winch readily 

 separate from one another and escape as individual 'spores' when the ascus 

 opens. 



The spores germinate in a very similar manner in the other species. In many 

 of them, those for instance which live on Poplars and Alders, a very large number of 

 small sprouting spores are found in the ripe ascus. Sadebeck states that these are 

 always sproutings from eight primary ascospores ; according to my earlier researches 

 and Brefeld's investigations, repeated quite recently, the original spores in Exoascus 

 Populi may be less than eight; Brefeld says that there are usually four, and I 

 -remember to have seen only two and three. Short germ-tubes, which soon give 

 off sprout-cells, are occasionally formed from the spores, as, for example, in E. 

 alnitorquus. 



Sadebeck has noticed that the products of the germination of the spores of. 

 Exoascus alnitorquus and E. bullatus penetrate into young leaves of Alnus glutinosa 

 or Pyrus communis, and there develope directly into ascogenous hyphae. The mode 

 of penetration is not stated. This observation would justify our assuming a similar 

 behaviour in the other species, with the addition that in some of them at least the 

 mycelium vegetates and maintains itself for a long time in the plant which it attacks. 

 For instance, it is found early in spring in the rind of the branches of Prunus and 

 spreads from them into the young twigs and fruits ; and in E. deformans, which 

 inhabits the cherry-tree, it is perennial and lives for years in the rind of the branches, 

 where it causes the ' witches' brooms,' and sends branches every year to form asci in 

 the leaves, which are disfigured in a similar manner. 



There is another doubtful Fungus which Reess has named Endomyces 

 decipiens, and which must for the present be placed near Exoascus. It grows in 

 old lamellae of Agaricus melleus and consists of septate hyphae, which are often 

 constricted at the septa and produce small ellipsoid asci arranged in lateral clusters. 



