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, which 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. 
