286 HOFMEISTER, ON 



spiral bands into which the outer membrane shortly after- 

 wards divides.* 



In those sporangia however in which some cells of the 

 outer membrane exhibit traces of elater-formation and others 

 do not, the capacity for distension of the middle membrane 

 is far behind that of the outer one. Even in the fluid con- 

 tents of the sporangium itself the outer membrane, in 

 JEqtiisetum limosum, is at a considerable distance from the 

 middle one. Upon treatment with alcohol the middle and 

 the inner membrane are drawn far away from the outer one 

 whilst they remain in close contact with one another, and 

 with the cell-contents. Upon the subsequent addition of water 

 the inner membrane remains still in close contact at every 

 point with the cell contents ; the middle one becomes some- 

 what detached and often irregularly folded ; and the outer 

 layer is far removed from the middle one. With this dis- 

 tension of the outer membrane it becomes manifest that 

 the latter is traversed by two left handed, parallel, spiral 

 lines, in the course of which the membrane is thinner than 

 in its other parts. In profile, i. e., in an optical longitu- 

 dinal section of the cell, I see with the best microscopes 

 that the thicker portions of the membrane protrude inwards 

 over the thinner parts (PI. XXXVIII, fig. 10), not out- 

 loardly^ as Sanio says (' Bot. Zeit.,' 1857, p. 661). When 



* In the c Vergleichende TJntersuchuugen, 5 p. 99, I spoke of the processes 

 above described as consisting of the formation of a free cell (the spore) around 

 the primary nucleus of the special mother-cell. In. opposition to this, Sanio 

 has shown ( c Bot. Zeit.,' 1856, p. 181, 1857, p. 657) that within the sporangium 

 the two membranes always lie close to one another, and that therefore a free 

 cell-formation cannot be admitted. This is quite correct. Sanio further 

 attempted to show that there could be no such thing as a centripetal spiral 

 thickening of the outer cell-membrane, which membrane at a later period splits 

 to form the elaters. The reasons brought forward to prove this are however 

 not convincing. During the development of the spores of the Equisetacea; 

 some phenomena occur which have au important bearing upon the study of the 

 cell-membrane, and I therefore give here in some detail the result of recent 

 investigations of this subject. Some of Sanio's objections to my views as to 

 the divisions of the mother-cell (1. c, 1856, p. 170) have since been abandoned 

 by himself (1. c, 1857, p. 658). With regard to his observations on the 

 abnormal development of certain mother-cells and the division of the primary 

 nucleus by constriction, I will only remark that there is no analogy between 

 such cases and the cases where the process of development is normal. 



-j- I contend that my representation ('Vergl. "Outers.,' t. xx, f. 18) is quite 

 correct, irrespective of the fact that in this figure the thin portions of the 

 membrane have come out disproportionately thick. 



