112 DIVISION I.—GENERAL MORPHOLOGY. 
A more noteworthy special case which recalls the formation of swarm-spores is 
that of the germination of the acrogenously formed spores (gonidia) of the plasmato- 
parous Peronosporeae (Peronospora densa, Rab. and P. pygmaea, Unger) ; here when a 
spore is placed in water the whole of the protoplasm suddenly swells and issues from 
the papilla-like tip of the spore which opens to admit its passage, and assumes 
the form of a spherical body, which invests itself at once with a new and delicate 
cellulose-membrane and then puts out a simple germ-tube. 
The number of the germ-tubes which proceed from a single spore is usually 
small, 1,2, or 3, seldom only afew more. The germination of the spores of the genera 
Pertusaria, Ochrolechia, Mass. and Megalospora, Mass., first observed by Tulasne? and 
more closely examined by myself®, is therefore all the more striking. These spores which 

Th N Wi7 






FIG. 37. a—d. Megalospora afinis, Kbr. aa ripe ejected spore. dd ives tages of germination on a moist 
microscopic slide; 4 and ¢ optical longitudinal sections only, ind the surface also is seen. e—/ Ochrolechra pallescens, Mass. ; 
efirst beginning of germination in optical longitudinal section, /with el d germ-tubes. g Pertusaria deBaryana, Hepp. ; 
optical longitudinal section through the half of a spore which is just beginning to i showing the canals with their 
enlargements in the wall The specimen was treated with glycerine; the wall with its cavities appeared when fresh as in 5; 
the contents of the spore are omitted. magn. 190, the other figures 390 times. 
are formed in asci (Figs. 57, 59 A, 2) are unusually large (in some species 180 » and 
more in length) and ovoid or ellipsoidal, filled with a dense oily protoplasm and sur- 
rounded by a thick colourless stratified membrane usually of many layers. Each spore in 
germination puts out simultaneously a large number, 50-100, of slender tubes, which 
either spring from all parts of the surface of the spore, as in Pertusaria, or only from 
the side which is towards the substratum. The tubes when formed have no special 
peculiarities. The formation of a tube begins with the appearance of a narrow canal 
running from the inner cavity of the spore in the outward direction, and passing at a 
right angle through the inner layers of the membrane. The extremity of the canal 
enlarges in the outer layers of the membrane and at their expense into a lenticular or 
spherical cavity, in which a homogeneous protoplasm collects, and the cavity at once 

* Mémoires sur les Lichens (Ann. d. sc. nat. ser. 3, XVII). 
? Pringsheim’s Jahrb. V, p. 201. 
