No. 2, September, 1920] PALEOBOTANY 261 



1987. Conklin. E. G. The mechanism of evolution. Sci. Monthly 10:496-515. 1920.— 

 At present there is not sufficient evidence to conclude that modifications of the cytoplasm of 

 the germ cells are ever really inherited or that they are the initial stages in evolution. — Almost 

 all the experimentally produced changes in chromosomes which are known to persist occur 

 during mitoses. — Variations in the volume of chromosomes are dependent upon the volume of 

 the resting nucleus and cytoplasm. These variations have no hereditary or evolutionary 

 value, as is evident from a comparison of the nuclei and chromosomes of the spermatozoa and 

 ova which differ in volume but not in value. — -Abnormalities in synapsis, separation :tnd equa- 

 torial division of chromosomes are much more important. The two former occur only in the 

 formation of germcells, the latter may occur in any cell. — Changes in the number of chromo- 

 somes are known in Oenothera, Ascaris, and Drosophila. — Changes in the constitution of 

 chromosomes by "crossing-over" of sections of homologous chromosomes or by fragmentations 

 or fusions so that a chromosome is not invariably composed of the same chromomeres has 

 been reported. — Experimental modification of chromosomes has produced monstrosities which 

 have not been carried to the next generation. But heat has been shown to increase the num- 

 ber of "cross-overs" in the oocyte of Drosophila. These are transmitted. Probably other 

 changes in the constitution of chromosomes may be traced to environmental influences. If 

 so initial stages in evolution may find their causes in such influences. — Genes seem to be sub- 

 ject to all the possibilities just discussed for chromosomes. — In conclusion, it is held that the 

 initial stages in evolution are caused by new combinations of chromosomes, chromomeres, 

 genes, subgenes, and that these new combinations take place in response to stimuli from the 

 external or internal environment. — Germ cells are so complex and so delicately adjusted 

 that they can not usually be greatly changed without rendering them incapable of continued 

 life. The future may show us methods of modifying germ plasm more delicate than those now 

 known. This would make a real experimental evolution possible. — The mystery of mysteries 

 in evolution is how germ plasm ever became so complex. The greatest problem which con- 

 fronts us is no longer the mechanism of evolution, but the evolution of this mechanism. 

 [See also next preceding Entry, 1986.]— L. Pace. 



1988. G., A. [Rev. of: Church, A. H. Thallassiophyta and the subaerial transmigration. 

 Botanical Memoirs, No. 3. Oxford University Press, 95 p. 1919.] Jour. Botany 58: 59-61. 

 1920. 



1989. Gothan*, W., and Nagel, K. Eine Zechsteinflora (Kupferschieferflora) aus dem 

 untern Zechstein des Niederrheins. [A flora from the copper shales of the lower Zechstein 

 in the lower Rhine region.] Gliickauf 56 6 : 105-107. 1 pi. Feb., 1920. — Discusses the occur- 

 rence of Ullmannia Bronni Goeppert, Ulhnannia frumentaria Goeppert, Voltzia Liebeana 

 Goeppert, Baiera digltata Heer, Callipteris Martinsii, and Sphenopteris sp., from the Permian 

 in the vicinity of Wehofen in Western Germany. — E. W. Berry. 



1990. Groves, J. A curious fossil Charaphyte fruit. Geol. Mag. 57: 126-127. 1 fig. 

 1920. — Describes specimens of what is probably Char a mcrianii Braun from the Miocene of 

 Locle, Switzerland, showing uniform tubular calcareous hollows on the inner side of the 

 spiral cells that form the oogonium sac. — E. W. Berry. 



1991. Guppy, H. B. Fossil botany in the Western World: an appreciation. Amer. Jour. 

 Sci. 49: 372-374. May, 1920. 



1992. Knowltox, F. H. Evolution of geologic climates. Bull. Geol. Soc. Amer. 30: 

 499-566. 1920. — Discusses the factors that might explain the prevailing uniformity of geo 

 logic climates, gives an extended summary of the bearing of fossil plants on past climatic 

 conditions, and concludes that the most probable explanation is earth control, the result of 

 internal heat, and not solar control which dominates existing climtitic distribution. — E. W. 

 Berry. 



