SECT. IT. COCCOCARPJEI. 307 



The fronds of the order Collemacei are gelatinous ; the 

 medullary stratum seems to occupy the whole, though 

 in two species of the genus there is a distinct epidermic 

 cellular coat. There are moniliform strings of minute 

 gonidia in the gelatinous matter, and others that are 

 single, arising from the division of each gonidium and 

 its supporting thread into two : both kinds differ jfrom 

 the gonidia in other lichens. The fruit-bearing discs 

 on the surface are open. Members of this order occur 

 in Europe, Africa, and Australia. 



The order Coccocarpei is mainly distinguished by 

 having orbicular discs entirely deprived of the cortical 

 envelope called an excipulum, or, if it does exist, it is 

 confounded with the thin membranaceous thallus. The 

 discs spring at once from the. medullary stratum, and 

 contain asci and sporidia, similar to those of minute 

 fungi (Sphserise). Some species of the genus Cocco- 

 carpia only differ from Lecidea in the total absence of an 

 excidium. The order is chiefly parasitic, and in some 

 cases the whole plant is little more than a mass of fruc- 

 tification, parasitic upon and continuous with the sub- 

 stance of other lichens, at whose expense they live, thus 

 forming an exception to the general habit of lichens, 

 which are fed by the atmosphere alone. M. Tulasne has 

 discovered that the genera Abrothallus and Scutula, 

 though consisting almost entirely of fruit, produce secon- 

 dary spores they are the only lichens in which they 

 occur ; while Phacopsis and Celidium bear spermato- 

 gonia, which, analogous to antheridia, contain minute 

 fertilizing particles. The parasitic genera occur in most 

 parts of Europe and North America. 



The Pyxinei are horizontal foliaceous lichens, for the 

 most part fixed by the centre. They have orbicular discs, 

 and form one of the most singular groups, both with 

 regard to the superficial fruit, and the curious con- 

 volutions of the perithecia. The fruit-cup, or excipulum, 



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