1894.] MICROSCOPICAL JOURNAL. 47 



crease the ease withwhich air is supplied and regulated. 



The part of the plant which is to be aerated is that 

 which is alive and active. Much of the tissue making up 

 a plant is not alive. It is the active protoplasm of living- 

 cells that is the seat of life in the plant and it is that 

 substance which must be both aerated and supplied with 

 water. The protoplasm of a matured active cell usually 

 assumes a definite form and arrangement of parts within 

 the cell-wall. The protoplasm constantly changes its 

 form as well as its chemical and physical properties but 

 nevertheless certain parts may be distinguished. These 

 are the nucleus and more or less clearly differentiated ecto- 

 plasm. The latter lies in very close contact with the cell- 

 wall in the living cell but contracts from it under the in- 

 fluence of certain reagents. Sometimes the ectoplasm of 

 adjacent cells are visibly connected. This continuity of 

 protoplasm occurs in the cortical tissues of many woody 

 plants and in the cribrose cells of the fibro-vascular 

 bundle. It has been asserted that the protoplasm of all 

 adjacent cells is continuous, the ectoplasm of adjoining 

 cells being connected by invisible threads. Some have 

 gone so far as to say that this can be demonstrated. The 

 irritability of plants, and the power which plants have of 

 absorbing and reforming their walls, can perhaps best be 

 explained upon this ground. 



It is to the ectoplasm and to the nucleus that whatever 

 the cell needs to live upon, must come. It was once be- 

 lieved that cutinized cell walls were impervious to gases. 

 This view is now abandoned. Grraham, an English phys- 

 icist and chemist, first formulated the laws upon which 

 the modern idea of the dialyses of gases permeating a 

 rubber membrane are based. Barthelemy hastened to 

 apply these laws to plant membranes such as the epider- 

 mis of the leaf or stem. He even intimated that stoma- 

 tes and other openings in cutinized membranes were of 

 minor importance to the plant in its exchange of gasses. 



