562 INTRODUCTION TO CRYPTOGAMIC BOTANY. 



investigation before he determines what are and what are not 

 good species. 



643. LyoopodiuTn catharticum has been celebrated as a 

 strong cathartic. Dr. Hooker has tried the dry plant and found 

 it inert, but so many drugs lose their virtues when kept beyond 

 a few months that we need not be surprised at the different 

 reports respecting this Lycopodium. Even our own L. Selago 

 has sometimes been used as a cathartic, and other species have 

 been employed in medicine. The inflammable nature of the 

 spores of L. clavatum has caused them to be used on the 

 stage to form artificial lightning. They are also employed 

 like liquorice powder to keep pills from adhering to each other. 

 If the fingers are rubbed with them, and immersed in water, 

 the fluid is so strongly repelled that it will not wet the skin. 

 Clubmosses are used in dyeing, to produce a blue tint. 

 They are sometimes of a deep red, a colour which is often par- 

 tially assumed by the tissues, and may possibly have other 

 virtues as dye-stuffs. 



644. Selaginella convoluta, like the rose of Jericho, has the 

 property of contracting into a ball when dry, and expanding 

 when moist. A singular phenomenon has been observed in a 

 species of Selaginella (S. mutabilis) cultivated at Kew. In 

 the morning the fronds are green, but as the day advances 

 they become pale, recovering gradually their colour by the 

 following day. Dr. Hooker has observed that in their pale 

 condition the endochrome of the cells of the leaves is con- 

 tracted into a little pellet. I have had no opportunity of 

 examining the matter myself, but I found in winter the paler 

 parts of the leaves to exhibit a contracted condition of the 

 endochrome, like that observed by Dr. Hooker. 



645. It remains only to say a few words respecting the fossil 

 forms presented by species belonging to this natural order. 

 These are amongst the noblest specimens of vegetation, and 

 weU deserve the attention of the botanist. Few points, per- 

 haps, have been more debated than the true affinities of such 

 plants as Sigillaria, Stigmaria, Lepidodendron, &c. If, 

 however, the structure of the stems be considered, and the 

 frmt of Lepidostrohus be allowed to belong to Lepidodendron, 



