THE ANNALS 



AND 



MAGAZINE OF NATURAL HISTORY, 



[THIRD SERIES.] 

 No. 12. DECEMBER 1858. 



XL. — On the Cainbium-lmier of the Stem of the Phnaerogamia, 

 and on its Relation to the Increase of Thickness. By H. von 



MOHL*. 



During the last tweuty or thirty years, investigations on the 

 development of the stem have led to the discoveiy that, in 

 spite of the great difference of structure in the stems of the 

 Monocotyledons and Dicotyledons, the course of their develop- 

 ment presents a far greater agreement than was formerly ima- 

 gined. Satisfactory as this progress is on the one hand, yet, on 

 the other, labourers in this field have, at least so it appears to me, 

 promulgated many erroneous theories ; hence a discussion of this 

 subject will not be inopportune. 



It will be most convenient to recur, in the first place, to 

 Schleiden's works. In his explanation of the peculiarities of 

 vegetable tissues f, he assumed the existence of three stages of 

 cell-development in the earliest period. In the first stage, the 

 new products present themselves in the form of an apparently 

 structureless, yellow, pultaceous mass ; in the second stage, in 

 which the process of cell-formation has just ceased, there is 

 a distinct delicate cellular tissue with more homogeneous con- 

 tents, which, however, is still completely saturated with sap ; in 

 the third stage, the cellular tissue assumes a blackish ai)pearance, 

 arising from the fact that all the intercellular passages are then 

 emptied of sap and contain only air. 



According to Schleiden's view, the arrangement of the cel- 

 lular tissue influences the conformation of tiie stem exclusively 

 in the first stage. This depends — 1. on the arrangement of the 



* Translated from tlio ' Bot. Zeitung,' xvi. p. 184 et spi/., June 25 and 

 July 2, 1858, by Arthur Ileiifrev, F.R.S,, &c. 



t Grundz. d. wiss. But. IBl.i. ii. 12/. 

 Ann. A,- Mag. N. Hist. Ser. 3. Vol. li. 27 



