ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 699 



to Fungi than to Algae. The formation of spores is especially checked 

 by these substances. Of mercuric chloride the optimum concentration 

 for Fungi is about 0*0013 p. c. ; of cupric sulphate about 0*012 p. c. 



Cryptogamia Vascularia. 



Megaspores of Isoetes and Selaginella.* — Herr H. Fitting describes 

 in great detail the structure and development of the megaspores and 

 me^asooranges in these genera, especially in relation to the mode of 

 growth of tbe cell-wall. The following are the more important results 

 of the investigation. The ditferentiation of the megaspore mother-cells 

 takes place, in Isoetes, at a much later period in the development of the 

 sporanges than has hitherto been supposed. The tapete-cells never 

 become absorbed ; in both genera they persist until the spores are nearly 

 fully ripe. In the spore mother-cells the first changes in the protoplasm, 

 which precede division, take place while the nucleus is still completely 

 at rest. The formation of the walls of the special mother-cells takes 

 place chiefly without assistance from the combining-filaments between 

 each pair of daughter-nuclei. The spore-wall consists, in both genera, 

 of several differentiated layers, which the author distinguishes as peri- 

 spore, exospore, mesospore, and endospore. The strongly silicified 

 perispore is formed later than tbe exospore, apparently at the expense 

 of the walls of the special mother-cells. As growth proceeds large 

 spaces are formed between the exospore and the mesospore on the one 

 hand and between the mesospore and protoplasm on the other hand ; 

 these are filled by a fluid which furnishes the material for the growth of 

 the membranes, which takes place by intussusception in both the outer 

 and the inner layers. Tbe plasmolytic condition of the cell forbids the 

 idea of the protoplasm taking any direct part in this growth. The 

 small amount of protoplasm in the spores immediately before they arc 

 ripe renders it scarcely possible that the nutrient fluid of the membranes 

 can be derived from it ; it is much more probable that it is the tapete- 

 cells which perform this function, since they behave like active gland- 

 cells. 



Sporophyll and Sporange of Isoetes. f — Mr. E. "Wilson Smith 

 publishes the results of a detailed series of observations on the struc- 

 ture and development of the sporophylls and sporanges of Isoetes echino- 

 spora and Engelmanni, of which the following are among tho more 

 important. 



The apex of the stem lies at the bottom of a funnel-shaped depres- 

 sion, round the sides of which the leaves are arranged spirally. This 

 depression is produced by the expansion of the cortical cells of the stem 

 in all directions. The air-cavities are formed out of four longitudinal 

 bands of cells. The ligulo originates in a single vesicular cell. The 

 mature ligule can be distinguished into four regions : the sheath, the 

 slossopode, a region of living cells, and a region of disintegrating cells. 

 The rudiment of the sporange is a transverse row of superficial cells 

 below the ligule ; there is no definite hypodermal archespore. 



* Bot. Ztg., lviii. (1900) l'^Abt., pp. 107-62 (2 pis.), 

 f L5ot. Gazette, xxix. (1900; pp. 225-5S, 323-4G (S pis.). 



