284 The American Naturalist. [April, 



takes place in direct opposition ton turgor force, that is, the 

 wall grows inward into a cell which is strongly turgescent. 



There is also one other ground for the position taken by 

 Schwendener's school in reference to the relation of turgor to 

 growth. This is certain facts connected with what is known 

 as "Gliding growth," " Gleitendes \Vachsthum." The prin- 

 ciple included in this idea may he briefly explained as follows: 



In the early stages of the secondary growth, during the time 

 when the new cells are receiving or taking on their final char- 

 acter as vessels and lihriform cells, etc., a growth takes place 

 by means of the walls of one cell gliding along the wall of 

 another. To explain this, it must be assumed that the walls 

 of the young cell consist of two lamellae ; whether this is so 

 from the beginning or not is entirely unknown, but at the stage 

 of the development where the gliding growth begins, the two 

 layers are there. These are not to be distinguished by the 

 highest power of the microscope, the wall appearing perfectly 

 homogeneous under the most powerful lens. The subsequent 



no other assumption could such growth lie possible. 



This assumption has also other and positive facts sustaining 

 it, besides the negative one mentioned above. In certain 

 cases the thin young walls of cambium cells have been proven 



Now according to this principle there must reside in certain 



mechanical one of pressure. In other words, there is an 

 active as well as passive condition of growth and this active 

 condition depends on certain properties of living matter and 



we know as mc-hanic-d 'force' Again' we are "brought to the 

 same conclusion as before, there is a force residing in living 

 matter of whose manner of action we are ignorant. That this 

 force exists in this matter we have certain' and positive proof. 

 This subject of turgor a~ before stated is one of the most 



standard on i tomena of growth. 



