152 M. Mohl on the Growth of Cell- Membrane. 



extent occupied by these vessels was obtained from the cells 

 lying next them*. 



a. Twig of Tilia parvifolia ; 1st internode 149 cells, 5th in- 

 tern. 110, 8th intern. 79, 13th intern. 29 cells. 



b. Twig of Robinia pseudo-acacia; 1st intern. 141, 5th 96, 

 10th 74, 15th 42, 20th 18, 23rd 9 cells, 



c. Twig of Gingko biloba; 1st intern. 42, 4th 36, 9th 17 

 cells. 



d. Twig of Morus alba. Here the interior portion of the vas- 

 cular bundle, which consists almost wholly of vessels, and in 

 which six or eight vessels lie immediately behind one another 

 in the radial direction, is excluded from the enumeration, and 

 only the number of the wood-cells is determined, which in every 

 internode lie outside this very conspicuous group of vessels : 

 1st intern. 228, 10th 134, 20th 58, 30th 2—3 cells. 



We arrive at similar results if we examine twigs which are 

 actually in a condition of rapid growth ; for instance, this was 

 shown by a twig of Hoy a carnosa about 2 feet long, the leaves of 

 which were yet all in the form of small scales; the 1st inter- 

 node 20 cells, 2nd 19, 3rd 17, 4th 12, 5th 7, 6th 4. In this 

 case the smaller number of ligneous cells in the upper internodes 

 could not at all be attributed to the circumstance that a larger 

 proportion of the cells were in the condition of cambium cells, 

 since in every internode only three to five cambium cells were 

 situated behind each other in the radial direction. 



Calculations instituted on other twigs and in other plants may 

 furnish other numbers ; but the great difference in the above 

 numbers renders it incontestable, that at the conclusion of the 

 first period of vegetation the upper and younger internodes con- 

 tain a much smaller quantity of ligneous cells in the radial di- 

 rection than the lower and old internodes of the same shoot ; 

 also, that during the greater proportionate length of the time of 

 vegetation in the lower internodes than in the upper, a very 

 evident multiplication of cells has taken place. 



As it may be objected to the result of the above enumerations 

 (though very falsely, since anatomical examination of young 

 twigs bears evidence to the contrary) that a greater number of 

 wood-cells already existed in a nascent state while the internode 

 was yet in the condition of bud, and that the greater number 



• I was originally undecided whether the vessels and cells should he 

 counted together or separately. Neither method however appears to me to 

 furnish so certain a result as that which I have followed, on account of the 

 irregular distribution of the vessels. At the same time, the very immaterial 

 relative differences which arise from these various methods of enumeration 

 are not worth consideration in reference to the general result. 



