330 THE MICROSCOPE AND ITS REVELATIONS. 



choosing its own Alga, just as the latter mostly attach themselves to 

 particular victims. "The peculiarity in the parasitism of the Lichen- 

 fungi lies in the fact that they are not attached to their host externally 

 at any one particular spot, and do not penetrate into its cells, but weave 

 themselves round them, and inclose them in their hyphal tissue." (Sachs, 

 loc. cit.) The formation of sexually produced ' spores' takes place in 

 asci or 'spore-cases/ arranged vertically in the midst of straight enlon- 

 gated sterile cells termed parapliyses, so as to form a layer that lies either 

 on the surface of cup-shaped receptacles termed apothecia, or is completely 

 inclosed within perithecia. Each of the asci contains a definite number 

 of spores (usually eight, but always a multiple of two), which are pro- 

 jected from the receptacles with some force; and their emission, which 

 seems to be due to the different effects of moisture upon the several layers 

 of the receptacle, is often kept up continuously for some time. The 

 formation of these asci, as in the case of the ordinary Ascomycetes 

 ( 318), is the result of a sexual union, which takes place between the 

 male spermatia and the female trichogyne. These spermatia are produced 

 within spermogonia, which resembles on a very minute scale the male 

 receptacles of the Fucacece ( 328); being budded off from the exterior of 

 the cellular filaments that line those cavities, and, when mature, escap- 

 ing in great numbers from their orifices. Having no power of spontane- 

 ous movement, they must probably be conveyed by the infiltration of 

 rain-water to a trichogyne (resembling that of the Ceramiacece, 330) 

 which lies imbedded in the tissue beneath ; and when they have imparted 

 their fertilizing influence to the contents of the ascogonium, at its base, 

 these develop themselves into a spore-bearing apotkecium the whole 

 mass of spores which this contains being the product of the cell-division 

 of the originally fertilized 



