62 COMPENDIUM OF GENERAL BOTANY. 



3. These two rather rare extreme cases are opposed by tlie 

 great majority of growing organs, in which development is a com- 

 bination of growth and cell-division. According to Sachs, an organ 

 (example : stem or root) in the process of development may be 

 divided into tliree regions: {a) the region of the apex with active 

 cell-division and slight growth (increase in volume), (h) the region 

 of intercalary elongation with enormous growth and moderate cell- 

 division, (<?) the region of completed growth. 



According to the heading of this short cliapter, the activity of 

 the vegetative area, with and without apical cell, would belong here. 

 Yet for reasons pertaining to the arrangement of this book this sub- 

 ject has already been touched upon in The Structure of Tissues. 



We may designate the above-mentioned vegetative points as 

 " embryonic areas" with terminal position; while those formative 

 tissues whose function it is to produce growth in thickness should 

 be designated as " internal " embryonic areas. From the activity 

 of these vegetative areas result the mechanical and vascular tissues, 

 and from a practical standpoint would be treated in the cliapter on 

 the tissues named. This also applies to the cork-cambinm. 



The formation of seoondary organs on pre-existing organs 

 (formation of organ-systems) will be more fully treated in a subse- 

 quent section. 



If, after the mere mention of these things, the reader should ask 

 why a chapter on the cell- forming function is at all introduced at 

 this point, the answer may be found in the following : 



A plant, whether it lives for a period of less than one year or 

 over one thousand years, is engaged in the formation of new organs 

 during the annual vegetative period of its entire existence. These 

 developing organs must have areas which are meristeniatic in char- 

 acter. The most important organs (leaves, branches, roots, fre- 

 quently vascular tissues, etc.) are not only formed once and endowed 

 with a lifelong function, but are increased in number by new similar 

 organs, and in the case of loss are uniformly replaced. Among 

 animals certain subordinate" organs, for example hairs, are endowed 

 with a lifelong power of regeneration. However, constant neo- 

 formation of the most important organs is not the rule, while the 

 vegetable organism is specially adapted in this respect. This 

 "function "is inherently peculiar. Its activity is perhaps not of 

 such great importance to the complete organism as, for example, 

 the activity of green cells (function of assimilation) ; it rather 



