No. 2, November, 1920] PALEOBOTANY 1 1 1 



This is Burbank's method of producing his "new creations in plant life." 1 1 is usually | 

 sible after a few generations to gel homozygotes thai breed inn' and in this way a ne^ variety 

 is established. These may be of evolul ionary value. Genuine mutants have now been found 

 in so large a number of plants and animals t hat it seems probable that all inherited differences 

 appeared in the first instance in this way. The rate at which mutations appear seems to dif- 

 fer greatly in different species. But they are probably of more frequent occurrence than ia 

 now known. Drosophila lias furnished the largest number of mutants now known. Many 

 of these contain lethal factors causing the early death of the individual. — Whether mutations 

 are caused by environmental conditions is at present unknown, although Muller and Alten- 

 btjrg found them more frequent at high temperatures. — Species are presumably the result 

 of the heaping up of viable mutations. The approximate number of known living and extinct 

 species in (lie different phyla of the animal kingdom differs very greatly, e.g., Protozoa 

 8000, Rotifers .".'id, Arthropoda 400,000, Pisces 13,000, Amphibia 1,400, Reptilia 3,500, Aves 

 13,0(H), Mammalia 3,50(1 11 is apparent that the number of species in a group is not dependent 

 entirely upon its age. Birds, which arose in Jurassic, have three times as many species as 

 Mammals, which appeared in Triassic. — The number of species is not dependent on the number 

 of individuals produced, nor upon their rate of reproduction. Birds, which are relatively few 

 in number of individuals and of eggs produced, have as many species as the much older class 

 of fishes, which lay perhaps a thousand times as many eggs. In general it seems that evolution 

 has been more rapid where fewer, better cared for young are produced. — Size does not seem 

 to be directly related to the rate of evolution, nor does it seem to be dependent always upon 

 changes in environment and diversities of habitat. Many paleontologists mention that the 

 rate and direction of evolution are determined by environmental changes and speak of "waves 

 of evolution." The number of mutations that survive and give rise to species is limited by 

 environment, that is by natural selection. Rate of mutation seems to depend upon the par- 

 ticular organization of the germplasm, some types being relatively stable with few mutations, 

 other types relatively unstable with numerous mutations. — The fact of survival is evidence 

 of adaptation, and the rate of adaptation does not seem to be proportional to the rate of repro- 

 duction, but rather to have gone farther in organisms in which the rate of reproduction and 

 of elimination is relatively slow. — Thousands of species appear which do not lead to any 

 increase in complexity. There are probably more than a million species and yet there have 

 been relativeby few lines of progress. Every mutant does not represent the beginnings of a 

 new path of evolution. Increasing complexity must have depended upon rare and fortunate 

 mutations which contained the possibilities of further evolution. Certain species *are too 

 highly specialized to give origin to new lines of progress. — The utmost limits of progressive 

 organization within the limits of a single cell were probably reached before Prbterozoic time. 

 Since that time the paths of progress are in multicellularity, multiplicity of tissues, organs 

 and parts, compound organisms, social evolution and rational evolution of human society. — 

 In conclusion, the suggestion is made that recent theories as to causes of evolution are not 

 wholly satisfactory. There may be important factors in evolution not yet "dreamed of in 

 our philosoph}'." — L. Pace. 



796. Davies, D. Distribution of the different species of flora and fauna from the West- 

 phalian and part of the Staffordian series of Clydach Vale and Gilfach Goch, east Glamorgan- 

 shire. Trans. Inst. Mining Eng. 59: 183-221. July, 1920.— A compilation of 25 years' col- 

 lecting from the Carboniferous of Wales, the fossil plants having been determined by R. 

 Kidston. These number 4000 specimens and their chief value lies in the careful stratigraphic 

 location of each, thus affording data for determining the range of the different species and 

 their value in correlation. — The forms enumerated comprise 12 species of Calamites, 1 of Equi- 

 setiles, 6 of Asterophyllites , 5 of Annularia, 9 of fructifications and miscellaneous calamite 

 remains, 5 of Sphenophyllum, S of Lepidodendron, 1 of Bothrodendron, 1 of Ulodcridron, 2 of 

 Lepidoploios, 4 of Lepidophyllum, 1 of Asolanus, 1 of Halonia, 4 of Lepidostrobus, 18 of Sigil- 

 laria, 2 of Sligmaria, 14 of Neuropteris, 1 of Zeilleria, 21 of Sphenopteris, 1 of Dolerophyllum, 

 1 of Alliopteris, 5 of Pecopteris, 4 of Mariopteris, 2 of Linopteris, 1 of Dactylotheca,2 of Crosso- 

 theca, 1 of Corynopteris, 5 of Alethopteris, 1 of Eremopteris, and a variety of seeds and miscel- 

 laneous remains. — E. W. Berry. 



