

154 BOTANICAL GAZETTE [February 



2. A real species is "a group of individuals of identical constitution, unable 

 to form more than one kind of gametes; all monogametic individuals of identi- 

 cal constitution consequently belong to one species." 



3. A "Linneon," says Lotsy, "is a vestigial group of a once much larger 

 group of differently constituted types, born of a cross, which is apt to simulate 

 a species by the overwhelming majority of the dominant types it contains, as 

 a result of free-intercrossing, combined with a favoring of the dominants by a 

 process of selection, weeding out the weaker or more conspicuous recessives; 

 this uniformity being more apparent then real, because pure dominants are 

 indistinctible, in most cases, from dominant-hybrids." 



4. In another place the author states briefly his idea of the causal factors 

 of evolution. "The vera causa of the production of new types consequently 

 is: crossing; the vera causa of their extinction: the struggle for life; the 

 selection resulting from the latter is by no means a revival, but is the sign of 

 the struggle of the doomed." Just what is meant one can only conjecture by 

 the context. 



In taking the position that no variations or mutations arise except as the 

 result of crossing and subsequent segregation, the author throws out of court 

 the mutants that have arisen in such carefully controlled experiments as those 

 of Morgan and his pupils on Drosophila. He challenges the reader to produce 

 a single case of mutation in a true species, which, according to him, is a type 

 that produces only one kind of gamete and shows no variability in Fj and F 2 

 generations. In other words, if a mutation does occur it may be taken as 

 prima facie evidence of impurity in the stock. Such an argument leads 

 nowhere. ' 



The author follows his theory to its logical conclusion and attempts to 

 show that even classes and orders must have been the result of crossing. We 

 fail to see the necessity of forcing a theory, that seems fairly reasonable when 

 applied within limits, to such an absurd length. If we object, we are told 

 that "a formation of new classes is not in action at the present moment, so 

 that it is illegitimate to claim that one who wants to explain evolution must 

 demonstrate how such a formation of new classes goes on." 



In conclusion, the reviewer would like to recommend the reader to the 

 second edition of this book, which, if it ever appears, will doubtless be a con- 

 siderable improvement on the first. — H. H. Newman. 



MINOR NOTICES 



Forestry for boys. — In a volume dedicated to the youth of America and 



manner 



the problems and processes of tree growth, forest development, and forest 

 utilization. The extent and economic value of our forests are well emphasized 



2 Moon, F. F., The book of forestry. 8vo. pp. xvii+315. figs. 64. New York: 

 Appleton. 1916. $1.75. 



