4 2 



botanical gazette, [February, 



rind pressure in this way : First, if this be the explanation, 

 then it must have its effect in the rind formation, that is, there 

 would also be year's rings in the tissues growing from the 

 opposite or phloem side of the cambium, which does not oc- 

 cur. Secondly, there must be a gradual going over to this 

 shortened diameter, as the pressure increases gradually. 

 This is not the case. Thirdly, the pressure of fissures made 

 in the rind by the frost is supposed to account for the dimin- 

 ished pressure in the spring time, but this fails to account for 

 the fact that in the hot zones year's rings have been known 

 to form the same as in colder climates. Russow suggested 

 that instead of pressure on the cells from without, it was 

 caused by a diminished turgescence within the cells, that the 

 decrease in the amount of nourishment was the cause of this 

 lack of turgor. Krabbe 9 next proved that the rind pressure 

 is only very little greater in the fall than in the spring, so lit- 

 tle as to make it impossible to be the cause of the short diame- 

 ter. Moreover, the rind being cut so as to lessen the pres- 

 sure rather tended to favor the production of the fall wood. 

 Next, Wieler experimentedas to the relative turgescence of 

 cells of spring andfall, and proved this to be about the same 

 during the entire vegetative period, therefore he claims there 

 must be some other cause for the manner of growth of fall 

 wood. He holds, with Russow, that the spring wood is bet- 

 ter nourished than that of the fall. 



In a review in the Bot.Centralblatt Bd. 34, no. 2,i888,Sanio 

 gives a brief summary of the conflicting opinions of Wieler 

 and Krabbe. The latter states, we have now two theories 

 as to the cause of the fall growth of wood, viz. : Wieler's 

 and Hartig's. Both claim it to be the varying conditions of 

 nutrition in the fall and summer : but the one, Hartig, says 

 the tree is better nourished in the fall than in the spring ; the 

 other holds the contrary opinion. Hartig claims that the 

 increased nourishment of the fall is used in adding to the 

 thickness of the wall : Wieler explains the shortened radial 

 diameter as due to the decrease in nourishment offered in 

 the fall, and that the thickness of these walls depends on 

 nourishment already acquired by the tree, and that their 

 growth in thickness is quite independent of their growth in 

 surface. He also claims that the greater or less number of 

 ducts is a thing " per se," that it is not a constant factor in 

 the problem, and does not attempt an explanation of this 



» Krabbe. Ueberdas Wachsthura des Verdickungesringes und der jungen Holzzellen 

 In seiner Abhangigkeit von Druckwirkung. Abhandl. d. Akad. d. Wiss. zu Berlin, 1884. 



