80 SUMMARY OF CURRENT RESEARCHES RELATING TO 



it arises from a zyc^ote which may also be haploid (e.g. Scinaia, in 

 which reduction-division is completed directly on germination) the 

 gonimoblast is haploid. Different cases are to be distinguished according 

 to whether the diploid sporophyte produces gonospores (mostly similar 

 to tetraspores) or tokospores (a new and degenerate expression coined 

 by the author for gonotokont-spores), or diplospores. These views are 

 also applied to the various families of plants. E. S. Gepp. 



Periodicity and Geographical Distribution of the Algae of Baden. 



A. Rabanus (Ber. Naturforsch. Freiburg i. Br., 1915, 21, 1-158 ; 



see also Bot Centralbl., 1917, 135, 389-91). The work has a 

 double aim : to give an insight into the periodicity of the algae during 

 the course of a year in various localities, and to give a geographical 

 account of the alg» of Baden. A resume of previous work on the 

 subject is followed by an account of the algal vegetation of the Black 

 Forest, the plain of the Rhine and the Kaiserstuhl. The difference in 

 the flora of the three regions arises from the differences of temperature 

 and the varying water-level. After describing the annual cycle of 

 algee in the various habitats, the author discusses their periodicity in 

 different localities— the ditches by the roadside in the plains, the 

 mountainous districts, rivers, ponds, marshes, etc. Most of the species 

 are too much (Ulothrix) or too little {Cylindrocystis) dependent on 

 outside factors to allow of an inherited periodicity in their life-cycle. 

 Only Spirogyra flourishes from autumn to spring, or only in the spring, 

 and mostly in puddles and ditches which are filled with water only in 

 the rainy season. The explanation of " water bloom " is still far to 

 seek. Certain algae retained life through a prolonged period of freezing, 

 and this is dependent not only on the degree of the frost, but on the 

 ^' mood " of the algal cell. The resistance to heat varied greatly, the 

 most sensitive being Ulothrix, in lesser degree Stigeoclonium and 

 Conferva ; Vaucheria can bear fairly high temperatures. Many other 

 interesting peculiarities are noted for various species. The geographical 

 distribution is fully treated. A list of species recorded for Baden is 

 given, and certain aberrant forms of Desmidiaceae are described, but not 

 named. Various results are shown in tabular form. E. S. G. 



Notes on Some Intermediate Forms of the Genera Navicula 

 and Cymhella. — Sir Nicholas Yermoloff {Journ. Quekett Microsc. 

 Club, 191H, 13, 18 pp., 3 pis.). The author shows by a process of 

 *' synthetic integration " that the fossil diatom Navicula mo}wiouthiana 

 may be considered as an ancestral form of a whole series of species of 

 VymbeUa, which he describes. The series ends in the very small C. 

 microcephala, the intermediate forms passing almost imperceptibly from 

 one to the other along the ladder. It is presumed that the parental 

 fossil form N. monmouthiana appeared about the end of the Pliocene 

 period in the State of Maine, and the descendant species have been 

 evolved during the sul)sequent Quaternary period up to the present 

 day. As regards the term "species," the author gives a definition 

 which was advocated in Russian scientific circles before the war : " A 

 .species in Nature corresponds to what in the Differential Calculus is 



