DISEASES OF PLANTS. 135 



to be made up of what are termed cells. These cells form organ- 

 ized structure. They are made up of the ash-constituents and the 

 vapor-constituents so intimately interwoven that they are both 

 essential to the vitality of the plant. These cells must be very 

 plainly described. They consist primarily of little spheres, or 

 globes, composed of two layers and liquid contents. The outside 

 layer is to protect the inner one ; the inner one is the growing 

 lining to which has been given the power of increasing in size and 

 number. The cell is, at first, a sphere, perfectly round in its 

 contour. Upon pressure the cell may be made to assume almost 

 any shape. Two cells lying together form one long cell, with a 

 double partition which may be broken down. Cells may be made 

 by pressure to assume a flat shape or a prismatic form. Out of 

 these cells all tissues of every part of the plant are made, even 

 the tubes or vessels in which part of the sap is conveyed being 

 formed out of contiguous cells which have lost their partition 

 walls. The living, or exterior cells are constantly producing new 

 cells for new tissue, while the older cells are packed away in the 

 interior of the stem to constitute that which we know as woody 

 fibre. I have said that these live cells are constantly producing 

 new cells in every exterior part of the plant. I should have said 

 provided the proper food is given to the plant and proper sur- 

 roundings such as light and air and moisture are secured, and 

 provided no new influence comes in to affect cell-growth. The life 

 and even the health of the plant depend upon the growth of these 

 primary cells. Any influence which destroys or disturbs cell- 

 reproduction has a direct effect upon the growth of the plant. It 

 is our purpose to see what influences there are in nature which 

 operate adversely to cell formation and multiplication, and in our 

 further progress I shall ask you to bear in mind several important 

 facts which we have noticed in our brief review. 



First, The fact of the existence of cells in every plant. 



Second, The fact that these cells are made up of fixed con- 

 stituents, such as salts of lime and soda, &c., and of volatile 

 constituents which are broken up and driven off at a high tem- 

 perature. 



Third, The fact that cells grow and multiply by means of the 

 formative power inherent in their lining, or inner layer. 



Fourth, The fact that influences which hinder cell-reproduction 

 affect unfavorably the growth of the plant ; and that upon the 

 health of the cell the health of the plant depends. 



