Development, and Structure of the Vegetate Cell. 2755 , 



fluid containing tannic acid is diffused. These lacteal vessels 

 resemble the ramified fibrous cells of the bark, in sending off 

 branches into the intercellular spaces, the membranes of which, 

 from their extreme tenuity, may be readily overlooked, and thus 

 give rise to the inference that the lacteal fluid circulates within 

 the intercellular spaces themselves. I believe I have proved in 

 that memoir that the lacteal vessels do actually possess walls of 

 their own ; they are therefore, with reference to their mode of- 

 origin, analogous organs to the fibrous cells of the bark. 



The processes which go on in the formation of the so-called 

 callics on the lower part inserted into moist earth are precisely 

 similar to this formation of periderm ; and this was particularly 

 the case in cuttings of Philodendron when these were terminal 

 shoots, and had continued to develope themselves after their 

 separation from the lower part of the stem. 



Under these circumstances also, a layer of cork is first pro- 

 duced on the cut surface (which, owing to its being implanted 

 in the moist earth, scarcely undergoes any desiccation), to pro- 

 tect the living tissues from the access of air. However, the 

 cork-lamina does not acquire the same proportion as in the pro- 

 cess of cicati'ization in the air, nor does it penetrate so deeply 

 within the plant-tissue near the epidermis and vascular bundles; 

 and after the peridermic layer has attained a certain thickness, 

 the cells formed deeper within the tissue, are not cork-cells, but, 

 like the cambium-cells of the apex of the axis, become converted 

 into the most various histological elements. 



Two cell-nuclei are frequently met with in one mother cell, 

 each containing either two nucleolar corpu^cleg or two vesicles 

 of a larger size and having each two nuclear* cells, whilst no 

 cell-nucleus belonging to the cell-system of the mother cell is 

 contemporaneous with them. 



Criiger, who first fully described (Botanische Zeitung, 1860, 

 p. 369) the changes in the cell-tissue during the formation of 

 callus, supposed that no new formation takes place in the cut 

 vessels. This, however, is an error ascribable without doubt to 

 the great tenuity of the walls of the endogenous cells, the 

 appearance of which is a counterpart of what has been already 

 described and figured (PI. V. figs. 3-5), except that these cells 

 are still more hyaline and transparent, inasmuch as they are 

 defended from the contact of the air, and consequently not ren- 

 dered suberous [verkorkt). 



I have found the vessels contiguous to the callus filled with 

 new cells, not only in endogenous but also in exogenous plants 

 — for example, besides Philodendron,iaZingiber,Drac(Ena,Zamia, 

 Cycas, Ficus, Gesneria, &c. In all cases the fully developed 

 vessels have a much greater tendency to generate new cells in 



