96 Dr. H. Karsten on the Sexual Life of 



result (not entirely borne out by facts) of later investigations 

 of the cuticle, has, in a new exposition of the structural relations 

 of the pollen, expressed hiins 'If somewhat ambiguously inspect- 

 ing them, and in such a way that his description has tended to 

 strengthen the prevailing erroneous hypothesis, that the outer 

 lamina of the epidermis (the cuticle) is produced from the sub- 

 jacent layer by a process of secretion or exudation. 



This theory of the growth of the cell by a simple act of de- 

 position or exudation, after having prevailed during the last 

 generation, must certainly be exploded ; for it is contradicted 

 by the progress of physiology. For though 1 was not able to 

 disprove it by the facts presented in my dissertation (De Cella 

 Vitali, 1843) and in other works, yet my repeatedly adduced 

 demonstrations respecting the origin of resin and of the wax-like 

 cuticular lamina of plants must convince every thinking person 

 that organization is not a mechanical but a dynamical or vital 

 act. (See ' Botanische Zeitung/ 1857, p. 313, and PoggendorfFs 

 'Annalen/ 1860, p. 640.) 



That the " dot-cells " which lie on the inner wall of the extine, 

 and at a later period effect its perforation, may produce a secondary 

 generation of cells, has just been remarked; and the same phe- 

 nomenon is also sometimes observed in the case of the porous 

 ligneous cells of the Coniferaj. This circumstance is very clearly 

 illustrated by me, in the fourth plate of the ' Flora Columbia?/ 

 in the figure of the pollen of a Bignonia, the membrane of which 

 is occupied by a large number of small, not quite flat, oval cells, 

 not in contact with each other. Further, each of these contains 

 a third generation of smaller cells, about sixteen in number, 

 and together form an envelope around the smooth enclosed in- 

 tine. After being macerated for a time in dilute sulphuric acid, 

 the cells of the second generation detach themselves from their 

 parent-cell, to the inner surface of which they were affixed, and 

 are seen floating freely about under the object-glass. The mem- 

 branes of these different generations of cells are in this case not 

 thickened : wei*e they so, we should have such forms produced as 

 are met with in Synanthereas, Nyctaginese, Convolvulacese, &c, 

 except that, in these, the cells of the second and subsequent gene- 

 rations become frequently converted into setse, which project 

 from the whole external surface of the extine, and are therein 

 analogous to what is so clearly demonstrable in the hairs of the 

 epidermis. Moreover, the structure of the spores of Cryptoga- 

 mia, so thoroughly investigated by Mohl, teaches us very di- 

 stinctly the signification of the reticulated surface of these bodies, 

 so nearly allied to pollen-grains, in all that relates to their mode 

 of development. This assertion is especially corroborated in the 

 case of the spores of Acrostichacese, Aspleniacese, and Aspidiacese, 



