340 



The Living Plant 



Such are the principal phenomena of that phase of growth 

 which is concerned with enlargement. Another phase is con- 

 cerned with the formation of new parts, or development. But 

 the relations of the two will be much plainer if, before proceeding 

 with the latter, I describe the cellular basis of both. As to this, 

 we may anticipate a little by saying that in general, enlargement 



Fig. 128. — A young leaf of Engliah Ivy marked in regular squares, and the same leaf a 



week or two later. 



depends upon swelling of cells already formed, while develop- 

 ment, or the construction of new parts, rests upon the formation 

 of new cells. 



The mode of formation of new cells is singularly uniform 

 throughout all plants. It takes place, as a rule, only in small 

 compact thin-walled cells densely filled with protoplasm, the 

 kind technically known as meristem and best shown at the growing 

 points of stems and roots (figures 53, 137, 139, C. D). The details 

 cannot be seen in living cells, but can be inferred from the appear- 

 ances presented by cells killed, stained, and sectioned for the pur- 

 pose. The first sign of new cell formation occurs in the nucleus 

 (figure 101), where the granules become more conspicuous and col- 

 lect into stout threads which then sort themselves out in the form 



