LIFE OF THE PLANT-CELL. 121 



Mohl very briefly adds the remark, that the development is also in 

 accordance with it. I believe that a thoroughly complete history of the 

 development of this structure would have been on all accounts of greater 

 importance than the most comprehensive observation of it in its com- 

 pleted state. I believe that H. Mohl will be obliged to admit with me 

 that all the completed forms may, in the absence of any preconceived 

 opinion, be explained at least as well according to my view. I believe, 

 however, that his mode of explaining this formation is met by insuper- 

 able difficulties in certain conditions, as, for instance, in Cycas revoluta 

 on account of the formation of the pores, which elsewhere universally 

 proceeds from the original cell-membrane. By far the most simple and 

 most natural explanation of this formation in Cycas appears to be the fol- 

 lowing : that on the one side (externally) a secretion has been deposited, 

 and on the other side (internally) a thickening of the original cell-mem- 

 brane has been effected by the formation of lamina, up to the commence- 

 ment of the pore-canals. In this case, also, the observation of earlier 

 conditions shows that the pores become visible at least simultaneously 

 with the commencement of the formation of the " cuticula," and probably 

 even somewhat earlier ; a fact that is totally irreconcilable with the view 

 advocated by Mohl. I must continue, for the present, to consider my 

 view as supported by the observation of the course of development of 

 the secreted layer. Especially do the observations on Oryza sativa, the 

 Hyacinth, and on Dipsacus fullonum, appear to me to afford sufficient 

 assurance of its being well founded. 



The second view has been proposed by Hartig (Beitrage zur Entwick- 

 lungsgeschichte der Pflanzen, 1843). He assumes that the first cell, the 

 foundation of the whole plant (primary cell), remains persistent, and 

 envelopes the entire plant, continuing to grow during the whole life of 

 the latter ; that it is sometimes drawn through the stomata into the 

 intercellular spaces, and is sometimes continuous over the stomata, 

 closing them up. * This primary cell subsequently acts like all other 

 cells ; that is, it secretes, as " ptychode," an " astathe," and " eustathe," 

 which would appear to be my " secreted layer," the history of the de- 

 velopment of which is given with perfect correctness, and accords with 

 mine. With respect to this it is to be remarked, that, in direct opposi- 

 tion to his entire view of the mode of formation of cells, Hartig in this 

 case assumes that the " eustathe" is formed before the " astathe ;" more- 

 over, although a secretion may be allowed to take place in the case- of 

 cells with amorphous contents, in which chemical changes are proceeding, 

 it cannot be admitted to occur in Hartig's imaginary primary cell, which 

 has no proper contents at all, but merely encloses the cells of which the 

 plant is constituted. Consequently, in this case the epidermis-cells must 

 have secreted exteriorly their proper " eustathe" and " astathe," and 

 then, by means of these and the ' ptychode" of the primary cell through- 

 out, also the "eustathe" and "astathe" of the primary cell. It will, 

 from what precedes, be already evident that this view is very obscurely 

 worked out, and consequently cannot in any way be derived from direct 

 observation. Moreover, it is again to be remarked that the existence of 

 the primary cell in the form of a membrane immediately superjacent 



* This double relation of the cuticula to the stomate is of itself in the highest 

 degree improbable, and is evidently only imagined in order to bring into accordance 

 \\-i.h the notion set up by him of the primary cell the incontrovertible fact that the 

 stomate, for the most part indubitably open, leads into the subjacent intercellular 

 space. 



