ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 875 



is prejudicial to tlie formation of meristem ; 2. Access of nitrogen 

 will induce an amerismatic prothallium to pass over into a merismatic 

 condition. 



The development of the reproductive organs on the prothallium 

 is closely connected with its nutrition. Amerismatic prothallia 

 produce antheridia ouly, never archegonia ; these latter organs being 

 produced only in the neighbourhood of a meristem. 



The author regards those prothallia of ferns which produce 

 archegonia only and no antheridia as exhibiting the first step in the 

 advance from the isosporous to the heterosporous Filicinese. 



Cell-division and Development of the Embryo of Isoetes lacustris.* 

 — Hofmeister formulated the general law that in cell- division each 

 newly formed division-wall stands at right angles to the direction of 

 the preceding most energetic growth. Sachs disputed this view ; 

 but Dr. F. Kienitz-Grerloff supports the previous view of Hofmeister, 

 adducing as evidence the following instances: — The processes of 

 division in filaments of Gladopliora, especially in the formation of 

 lateral branches ; the division in the apex of a shoot of Metzgeria ; 

 the processes in the apical cell of a young rudiment of the sporo- 

 gonium of ArchicUum pJiascoides, which divides by walls inclined in 

 two opposite directions ; the cone of growth of Salvinia exhibiting a 

 similar structure ; the breaking up of the apical cell of Cladostephus, 

 on the cessation of growth at the apex at the commencement of the 

 dormant season ; the development within the apical cell in older 

 prothallia of ferns and in embryos of mosses, which determines the 

 direction of the division- walls ; the formation of the cap-cells and of 

 segments in roots with a three-sided pyramidal apical cell ; as also in 

 segment-cells generally. 



The interior of the macrospore of Isoetes lacustris is occupied by 

 moderately large roundish cells, each having a nucleus ; no dia- 

 phragm, like that of Selaginella, could be detected. Older unfertilized 

 prothallia had from twenty to thirty archegonia. The first division- 

 walls in the embryo divide it into octants. The cotyledon is formed 

 out of the two anterior and upper octants ; the first root out of the 

 two posterior and upper ones ; the foot out of the foui" lower octants. 

 The further cell-divisions are followed out in detail. 



The examination of the ripe and half-ripe spores is attended with 

 great difficulty; the author has not found any hardening material 

 adequate for obtaining good sections, and at the same time giving 

 sufficient clearness to the preparation. Soaking for a time in glycerine 

 answered for certain purposes. 



Muscinese. 



Chemical Composition of Mosses-t— E. Treffner has investigated 

 the chemical composition of several species of moss. He finds the 

 amount of silica always high, and varying but little in diiferent 

 species ; the greatest quantity was found in Funaria. Orthotrichum 



* Bot. Zt?., xxxix (1881) pp. 761-70. 785-95 (1 pi.). 



+ E. Treffner, 'Beitrage zur Chemie der Laubmoose,' 62 pp., Dorpat, 1881. 

 See Bot. Centralbl., ix. (1882) p. 9. 



