ZOOLOGY ANh BOTANY, MICROSCOPY, ETC. 685 



The cell is in all cases enclosed in a distinct cell-membrane ; naked 

 protoplasts do not occur in the Schizophyceaa ; a cell-membrane is 

 present even in the hormogones. The gelatinous envelope and the 

 sheath both take part in the formation of this membrane. Both the 

 sheath and the cell-membrane are marked by their strong resistancy to 

 chemical reagents, resembling in this respect the cuticle of the higher 

 plants ; but in optical and chemical properties they have nothing to do 

 with the cuticle ; they are chiefly composed of chitin. The cell-wall of 

 the heterocysts is, however, always composed of cellulose. 



The protoplast of all Schizophyceaa is differentiated into a peripheral 

 layer which contains the pigment, and a colourless central portion. The 

 pigment is usually present in the form of very minute granular bodies ; 

 each particle contains both chlorophyll and phycocyan [in the Phyco- 

 chrornaceae] ; they must be regarded as chromatophores, and the author 

 terms them cyanoplasts. The cells of the Schizophyceae contain no 

 starch or starch-like substance, but glycogen has frequently been de- 

 tected ; this substance is the first recognisable product of assimilation in 

 the Cyanophyceas. 



The peripheral layer of protoplasm which contains the cyanoplasts 

 encloses two different substances, proteid-crystalloids and mucilage- 

 vacuoles. The proteid-crystalloids occur most largely in the heterocysts 

 and spores, being often entirely wanting in the vegetative cells of rapidly 

 growing filaments. Neither of these substances has any relations to a 

 nucleole. 



The central colourless portion of the cell of the Phycochromaceas 

 is a true nucleus. The cell invariably contains a single nucleus, with 

 the exception of the heterocysts, in which it degenerates at an early 

 period. The form depends largely on the dimensions of the cell. In 

 resting cells it consists of a slightly stainable ground-substance, in 

 which are imbedded small granules, identical with the chromatin 

 granules of the higher plants. These nuclei are distinguished from 

 those of the higher plants by the absence of nucleoles and of a staiuable 

 nuclear membrane. They are, however, sharply differentiated from the 

 cytoplasm. In the process of division the polar separation of the 

 chromatic substance and the development of a chromatic figure agree, in 

 all important points, with the karyokinetic process of division of the 

 ordinary vegetable or animal nucleus. 



Nostoc punctiforme.* — Pursuing his investigations on the power of 

 this organism to assimilate in the dark, E. Bouilhac states that glucose 

 may be replaced, as the nutrient material, by saccharose, maltose, or 

 starch, but not by levulose. The substances which serve for the de- 

 velopment of the plant are those which easily give rise to glucose by 

 hydrolysis, produced probably by the bacteria which accompany it, or 

 by the Nostoc itself. 



£. Schizomycetes. 



Structure of Bacteria. t — Prof. K. Nakanishi, by adopting a special 

 method of staining, found that all bacteria, when in the fresh condition, 



* Comptes Rendus, cxxxiii. (1901) pp. 5;~>-7. Cf. this Journal, 1898, p. 574. 

 t Centralbl. Uakt., 1" Abt., xxx. (1901) pp. 97-110. 145-58, 193-201, 225-32, 

 (5 pis. and 38 figs.). Cf. this Journal, 1900, p. 525. 



