3Ss 



THE AMERICAN NATURALIST [Vol. XLIV 



proportion are northern. In short, although as far as 

 phamogams are concerned the "Species Plantarum" in- 

 cludes characteristic representatives of different parts 

 of the world, as far as the Bryophytes and Thallophytes 

 are concerned it represents only a limited European 

 flora. 



The question may perhaps be asked by those who have 

 not studied specially any group of non-vascular crypto- 

 gams: Although the number of non-vascular crypto- 

 gams in the "Species Plantarum" is very much smaller 

 than that of phamogams, is it not perhaps the case that 

 the ratio represents approximately the relative size of 

 the two groups in nature? It has been the custom to 

 state that the phamogams outnumber the cryptogams, 

 some even saying that they are much more numerous. 

 Such statements are based solely on an enumeration of 

 described species and fail to give information as to the 

 probable actual number of species. It is not possible to 

 give figures on the subject which are up to date and the 

 statistics of even a few years ago are of slight value, for 

 it is only within a few years that the study of cryptogams 

 has been pursued in other parts of the world than Europe 

 or, to a less extent, North America. We can probably ob- 

 tain a more correct opinion if we consider probabilities. 

 The number of known species of Musci and Hepatica? has 

 been very much increased in the last few years, and al- 

 though the bryological flora of Europe and North Amer- 

 ica is now so well known that no very large number of 

 new species is to be expected there, in other parts of the 

 world and especially in the tropics, it is evident that the 

 work of exploration conducted by trained specialists will 

 bring to light a very large number of new species. The 

 same is true of lichens. In alga? a very great increase of 

 species is less to be expected, partly for the reason that 

 the region of growth of marine algse, pelagic species ex- 

 cepted, is more limited than that of land plants. But 

 even in alga?, it is probable that the known species will 

 be considerably increased. 



