880 INTRODUCTION TO CRYPTOGAMIC BOTANY. 



They are frequently strictly linear, and of very different length, 

 whether straight or curved, but they are also rounded at either 

 end, and oblong or elliptic. They are immersed in a thin 

 gelatinous mucilage. In some species the cavity is traversed 

 by anastomosing threads, as in Ramalina farinacea, while in 

 other cases, as in Parmelia physodes, there are articulated 

 paraphyses, the terminal joints of which are the largest. They 

 have never yet been found to possess flagelliform appendages, 

 nor have they any true motion, though, like other minute 

 particles, they occasionally exhibit the Brownian molecular 

 activity. If they are really capable of impregnation, they 

 probably act upon the sporidia when already formed, as the 

 spermatozoids do on the spores of Algae. There is no reason 

 to believe, as has been asserted, that they cause the formation 

 of the sporidia. 



420. In all those cases where similar bodies have been ascer- 

 tained to exercise sexual functions, the bodies are developed 

 within peculiar cells, and the remark may be extended to the 

 animal as well as the vegetable world. This difference is, how- 

 ever, no conclusive proof against their functions, though it 

 appears to me quite as probable that they should be a mere 

 secondary form of fertile fruit, as sexual organs. I do not 

 think it necessary to describe at length the notions of Bayr- 

 hoffer, as they are inconsistent with facts, and are either mere 

 theories, or rest upon imperfect observations. 



421. Every Lichen consists of at least the external, gonimic, 

 and medullary strata, beyond which there is frequently another 

 gonimic stratum, and basal cells or filaments. Both the true 

 fruit and gonidia proceed from the medullary layer; of which, 

 in point of fact, the other coat is a continuation only ; the 

 threads of which it is composed being condensed into a close 

 stratum so as to be hard and horny, and to present an appa- 

 rently cellular mass. The fruit, however, seems in no case to 

 be formed immediately from the external stratum, though both 

 in the spermatogonia and perithecia there is a compact cellular 

 stratum, giving rise immediately to the fertile sporophores or 

 asci, which simulates in point of structure the external coat. In a 

 similar way the inferior stratum is formed by the lower portion 



