ZOOLOGY AND BOTANY, MICllOSCOPY, ETC. 581 



Calcareous Nodules.* — 0. Penzig describes some ellipsoidal 

 calcareous nodules, 0*5-2 "5 cm. in length, from the mountain stream 

 Secca, north-west of Genoa. In the bed of the torrent are found small 

 basins, not exceeding a metre in diameter and 10-30 cm. deep, where 

 the water is limpid and calm ; at the bottom of these the nodules are 

 found. They are therefore not formed by the action of the water, but 

 are concretions generated in situ, around fragments of herbaceous plants. 

 Round this centre the lime appears to be slowly deposited. If the 

 nodules are dissolved in acid, however, it is found that surrounding the 

 vegetable fragment constituting the centre there is a mass of gelatinous, 

 delicate, greyish substance, composed of entangled minute filaments, 

 reproducing exactly the form of the nodule. They constitute almost 

 exclusively the organic base of the nodules, and are composed of masses 

 of Streptotli.rix lujalina Miguia. The part which this organism takes in 

 the formation of the nodules is difficult to determine, but there would 

 appear to be a genetic connexion between the bacterium and the 

 inorganic mass. Possibly the Streptothrix develops on the plant- 

 fragments in the water, and round the mass thus produced are deposited 

 the molecules of calcium carbonate. Thus, while the colony of bacteria 

 grows in size, the nodule keeps pace with it. This may be the result 

 of a purely mechanical action ; or it may be that by means of some 

 physiological process the filaments of StreptotJwix play an active part in 

 the precipitation and deposition of calcium carbonate. In all cases of 

 calcareous nodules hitherto recorded, species of Schizophycea? have been 

 present, belonging to Oscillariacete, Rivulariacese and Scytonemacese. 

 They have played an active and important part in the formation of 

 other calcareous incrustations. But never has any bacterium been 

 recorded other than free and without calcareous incrustation. 



Chara crinita.f — A. Ernst has made a study of Chara crmto, which 

 since the investigations of A. Braun (1856) and Migula (1888-1890) 

 has been recognized as an example of true parthenogenesis in the vege- 

 table kingdom. The author has made fresh cultural experiments and 

 cytological investigation, and he asserts as the results that in this plant 

 somatic parthenogenesis (ovogenous apogamy), not generative partheno- 

 genesis, occurs. This is contrary to the view held hitherto, but is in , 

 accordance with what is found among Angiosperms. 



Alternation of Generations in Floridese.J — N. Svedelius discusses 

 the problem of the alternation of generations in Florideaj. He opens 

 his paper with an historical account of tlie work done on the subject, 

 beginning with Camerarius at the end of the 17th century. He then 

 proceeds to give an account of the position of the reduction-problem and 

 the alternation of generations in Floride^e, the pioneer work of Niigeli, 

 Bornet, Thuret and Schmitz, etc., being followed by the younger investi- 

 gators, including the author himself. The results of each writer are 

 described and illustrated by figures. The conclusion of all the work 



* Malpighia, xxvii. (1916) pp. 401-5 (1 pi.). 



t Act. Soc. Helvet. Sci. Nat., Session 97 (1915) p. 198. 



X Naturw. Wochenschr., n.f. xv. Nos. 25-6 (1916) 40 pp. (14 figs.). 



