wound various branches and stems with twine, and in the results 

 given by the microscopical examination at different periods of subse- 

 quent growth he enumerated the 3 following pertinent principles: 



1. The growth of the wood elements in the radial and in the 

 tangential direction is influenced by the pressure under which it 

 takes place ; the greater the pressure the more feeble will be the 

 expansion. 



2. The number of successive divisions in the cambium depends 

 on the radial pressure then present; other things being equal, the 

 greater this pressure, the fewer will be the divisions in a radial series. 



3. The proportion of the number of vessels to the number of 

 wood-fibres in a ring depends on the pressure under which the ring 

 has been formed; the greater the pressure the less favorable is the 

 proportion to the number of vessels. 



Krabbe l by a peculiarly constructed chain working over brass 

 strips laid on the bark of trees was able to apply a graded and 

 definite radial pressure. His chief result was the proof that normal 

 cortical pressure does not effect the building of the annual rings ot 

 trees. Aside from this he obtained some results which bear directly 

 upon work recorded in the present paper . These results however 

 include numbers 1 and 2 given above as already contributed by de 

 Vries. In addition, Krabbe found 



1 . That in trees of neither Conifers nor Dicotyledons would the 

 cambium cells under any amount of pressure divide at a smaller size 

 than normal. 



2. That in Conifers a pressure of from 3 to 5 atmospheres, in 

 Dicotyledons of 5 to 7 atmospheres is required to lessen either in 

 number or size the elements arising from the cambium. 



3. That from the pressure last named growth would proceed up 

 to a pressure of 10 atmospheres in Conifers and 15 in Dicotyledons, 

 but would proceed more slowly. 



4. That in dicotyledonous trees as soon as the pressure had passed 

 a certain height — usually 1 atmospheres — an active cork meristem 

 was formed in the cortex. 



The work of which the following pages are a record was done 

 in the winter semester of 1892 and the summer semester of 1893, 

 in the Botanisches Institut at Leipzig, under the direction of Professor 

 Pfeffer, for whose able guidance and kindly bearing the Author feels 

 himself greatly indebted. 



Ueber das Wachsthum des Verdickungsringes und der jungen Holzzellen in 



seiner Abhangigkeit von Druckwirkungen. Berlin 1884. 



