INTRODUCTION TO CItYPTOaAMIG BOTANY. 



375 



development of the filamentous element of Strigula, a genus 

 in which the cortical element usually prevails. Ccenogonium, 

 on the contrary, appears to be a normal form, remarkable for 

 the almost total suppression of the upper stratum. The place 

 of growth is similar to that of Dictyonema, and its habit is 

 very much the same. It is just possible that the various 

 species of Chroolepus, which have some resemblance to Cepha- 

 leurus (Fig. 81, a), may be peculiar states of certain Lichens, 

 their reproductive bodies being very similar. 



Fig. 79. 



a. Section of a Collema, showing new fronds arising from the sur- 

 face. From Noukaheva. 



b. Sporidlum of Biatora marginiflexa, Bab. From New Zealand. 

 Communicated by Dr. Hooker. 



c. Leptogium bullatum, showing a section of one of the apthoiis pro- 

 cesses with its fertile disc, the sporidia and external cells of the 

 frond. More or less magnified. From Assam. Communicated by Dr. 

 Hooker. It is the form figured by Swartz, in Lioh. Amer. 



411. If the CoUemals are associated with Lichens, which 

 appears to me the most natural arrangement, we have still, in 

 most cases, the medullary and cortical layers with gonidia, dis- 

 posed frequently in long moniliform threads (Fig. 79, a) ; but we 

 have in addition an abundant gelatinous element, in consequence 

 of which, many are hard and rigid when dry, and when moist- 

 ened resemble closely some of the Algas. Indeed, some states 



