XXX11 



of cells constituting the neck of the organ which Hofmeister after- 

 wards proved to be ati archegonium. 



The stage of Nageli's work has now been reached at which he more 

 especially devoted his energies to the study of the Algae ; and a brief 

 sketch of the results attained in this direction will not be out of place 

 in view of the general biological importance of some of his observa- 

 tions, and of the basis which they afforded for his investigation of 

 other families of plants. The ' Zeitschrift fur wiss. Botanik,' in 

 addition to incidental observations on Algae in some of the other 

 papers, contains four which are exclusively algological : these are 

 " Caulerpa prolifera" (Heft 1) ; " Wachsthumsgeschichte von Deles- 

 seria hypoqlossunn" (Heft 2); " Polysiphonia" and " Herposiphonia " 

 (Hefte 3 and 4). The first of these is of importance in that it gave 

 an insight into the structure, not only of this remarkable plant, but 

 also of the whole family, the Siphoneae, of which it is a highly- 

 developed representative ; it proved that here the whole plant, 

 though attaining a considerable size, and exhibiting unmistakable 

 morphological differentiation into stem, leaf, and root, consists of a 

 continuous mass of protoplasm, unsegmented by cell- walls, and may 

 be termed "unicellular," as Nageli termed it, though subsequent 

 investigation has shown it to be multinucleate. The paper on 

 Delesseria, though of but slight algological interest, is, however, 

 really epoch-making, in that it gives the first account of growth by 

 means of a single apical cell, a discovery w T hich was confirmed by his 

 subsequent observations on Polysiphonia and Herposiphonia (see also 

 " Wachsthumsgeschichte " of Pterothamnion and of Hypoglossum 

 Leprieurii, in ' Pflanz. Physiol. Unters.,' Heft 1, 1855). His papers on 

 these two Algae are of peculiar importance, in that they manifest a 

 clear recognition of the fact that (see especially p. 220, and Plate VII, 

 figs. 1, 2, 3), in the Morideae at least, the cell-walls are porous, and 

 that the cytoplasms of adjacent cells are connected by protoplasmic 

 filaments passing through the pores of the intervening walls ; demon- 

 strating, in fact, that "continuity of protoplasm" which has been 

 rediscovered and studied during the last ten years. The algological 

 interest of these two papers is also great, for they contain some of 

 the earliest observations on the antheridia of these plants, on the 

 tetraspores, and on the cystocarps (as they had been termed by 

 Kiitzing), which Nageli considered (see Heft 1, p. 47) to be recep- 

 tacles for gemmae, as in Marchantia, and consequently termed 

 " Keirabehalter." At this period he does not express any opinion as 

 to the sexuality of the Florideae ; the first definite statement on the 

 subject, unfortunately quite erroneous, occurs in "Die neuern Algen- 

 systeme" (1847), where he separates the Florideae from the rest of 

 the Algae (including herein the Lichens) on the ground that the latter 

 are destitute of sexual organs, whereas the former possess them in 



