1917] AGRICULTURAL BOTANY. 433 



are perpetuated by heredity, natural selection being the cause not of their 

 origin but of their gradual extinction. It is considered correct, in a sense, to 

 say that species are related to one another in the same way that human 

 brothers or cousins are, being in each case simply separates resulting from a 

 previous crossing. 



The bearing of some general biological facts on bud variation, E. M. East 

 (Amer. Nat., 51 (1911), No. 603, pp. 129-14S).— The author, dealing with the 

 possible relation to bud variation of such conditions as environment, mutila- 

 tions, diseases, and changes in food supply, states that bud variations are 

 comparable to seed variations in their nature and in the abundance of types 

 produced thereby, but handicapped by the fact that recombinations of variant 

 characters are possible only in case of sexual reproduction. It is held that 

 environment must have been an immense factor during the long periods in- 

 volved in organic evolution, but its effects are shown so infrequently that it may 

 be neglected for the practical purposes of plant breeding. It would not, how- 

 ever, be safe to deny importance to bud variation as an adjunct to plant 

 breeding. 



Mendelian factor differences v. reaction system contrasts in heredity, I, 

 II, T. H. GooDSPEED and R. E. Clausen (Amer. Nat, 51 (1917), Nos. 601, pp. 

 Sl-Jf6; 602, pp. 92-101). — In this work, which besides listing related contribu- 

 tions deals with a number of facts and conclusions drawn from contributions 

 by Goodspeed, alone or with others (E. S. R., 34, p. 136; 37, p. 225), it is 

 stated that Nicotiana sylvestris, when crossed with varieties of N. tabacum, 

 gives an Pi hybrid which is a replica, on a large scale, of the tabacum variety 

 employed. Such hybrids produce a small number of functional ovules which 

 represent the sylvestris and tabacum extremes of a recombination series, most 

 members of which fail to function because of mutual incompatibility of the 

 elements of the two systems. Back crosses with sylvestris give both sylvestris 

 and aberrant forms, of which the former only are fertile and breed true. Back 

 crosses with tabacum produce apparently only tabacum forms, some of which 

 are fertile and breed true. 



The authors reach the general conclusion that Mendelian factors may be 

 considered as making up a reaction system, the elements of which exhibit 

 more or less specific relations to one another. Strictly Mendelian results are 

 to be expected only when the contrast is between factor differences within a 

 common Mendelian system, as ordinarily in varietal hybrids. When distinct 

 reaction systems are involved, as in species crosses, the phenomena are to be 

 regarded as a contrast between systems rather than between specific factor 

 differences. Sterility in such cases depends upon nonspecific incompatibility 

 between elements of the systems involvetl, and its degree depends upon the 

 degree of incompatibility rather than upon the number of factors. The con- 

 sequences of the application of such a conception to the complex type of be- 

 havior in CEnothera are pointed out and the suggestion is made that the type 

 of behavior exhibited by CE. lamarckiana and its segregants in hybridization 

 may be referred to such complex system interactions. 



CEnothera mutants with diminutive chromosomes, Anne M. Lutz (Amer. 

 Jour. Bot., 3 (1916), No. 9, pp. 502-526, pi. 1, figs. 7).— In this report, the first 

 of a projected ?eries of three on studies continuing for several years in Europe 

 and America and dealing with somatic chromosome number in mutants of the 

 lamarckiana group of CEnothera, the author considers the 14-chromosome mu- 

 tants, the 14+i-chromosome mutants and offspring of certain hybrids, the origin 

 of the small chromosome and its fate in succeeding generations, chromosomal 

 individuality as evidenced by the small chromosomes, and some observations 

 on (E. rubrinervis. 



