APPENDIX. 289 



case real death is induced. That which is exceptional, 

 therefore, in these species is, that desiccation in their 

 case produces merely a sort of syncope from which they 

 recover on being supplied with water. 



A certain number of the lower plants present pheno- 

 mena precisely similar to those which we have described 

 in the case of animals. We may here specially instance 

 the Nostoc, one species of which is not uncommon. This 

 Alga when well developed presents itself under the form 

 of brownish or dull green folded or even crumpled 

 patches, about one-fifth or one-sixth of an inch in thick- 

 ness, and sometimes as much as from two to three inches 

 in diameter. These patches shrivel up under the action 

 of dryness, until they are scarcely visible, but a shower 

 of rain is sufficient to restore them to their former 

 dimensions.* It follows from the experiments of Spallan- 

 zani and of Leman that when the Nostoc is dry, vegeta- 

 tion is arrested, and that it recommences as soon as the 

 organism is again furnished with water. We think, 

 however, that the observations which have been made 

 on this plant are scarcely so precise as those on the 

 Rotifers and Tardigrades. 



NOTE in. 



We draw a distinction in physics between the simple 

 microscope, and the compound microscope. The former is, 

 in fact, nothing more than a lens constructed of one or two 

 glasses. In this instrument the observer looks directly 



* M. Dujardin has made us acquainted with the extremely 

 simple structure of the Nostocs. The entire plant is formed of 

 strings of greenish microscopical globules immersed in a trans- 

 parent mucilaginous substance. (See Memoire sur le Nostoc, and 

 le Manuel complet de V Observateur au Microscope, by M. F. 

 Dujardin.) 



VOL. I. U 



