I I 2 



DIVISION I. GENERAL M< ilil'lIOLOGV. 



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 Peronosporeac (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 a few more. The germination of the spores of the genera 

 Pertusaria, Ochrolechia, Mass. and Megalospora, Mass., first observed by Tulasne 1 and 

 more closely examined by myself 2 , is therefore all the more striking. These spores which 



. Kbr. a a ripe ejected spore, b — d successives tages of germination on a moist 



mice ectionsonly, inrfth* -/OckroU 



c firs' tubes, g Pertusai 1 1, Hepp. : 



inn through the half ofa spore which is just beginning to germinate, showin with tlicir 



• ■iiirnts in the wall Thespi I with its cr tred when fresh as in A ; 



the contents of the ,/magn. 1 



formed in asci (Figs. 57, 59 A, B) are unusually large (in some species 180 ^ and 

 more in length) and ovoid or ellipsoidal, filled with a dense oily protoplasm and sur- 

 rounded In* a thick colourless stratified membrane usually of many layers. Ea< h spore in 

 germination puts out simultaneously a large number, .-,0-100, 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 die substratum. The tubes when formed have no special 

 pei uliarities. The formation ofa tube begins with the appearance ofa narrow canal 

 running from the inner cavity of the spore in the outward direction, and passing at a 



. 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 colle< ts, and the cavity at once 



1 Memoires sur les Lichens (Ann. d. sc. nat. *cr. 3, XVII). 

 I 'ringsheim's [ahrb. Y. p. 201 . 



