TISSUES AND SIMPLE ORGANS. 61 



X. Storing of food-substances. 

 XI. Secretion and excretion. 

 XII. Reproduction. 



As a final chapter to Functions II, III, and IV there will be 

 added a discussion of the " endoderm," or " protective sheath." 



SPECIAL FUNCTIONS. 



I. THE FUNCTION OF FORMATIVE TISSUES (MERI- 

 STEM AND CAMBIUM). 



The process of cell-division during the development of countless 

 plants and plant-organs is the principal cause of growth. Growth is 

 not equivalent to cell-division. But in the majority of the so-called 

 higher plants the function of growth stands in close interrelation to 

 the function of cell-division. Cell-division without growth, that is, 

 without increase in volume, is possil)le. It is, however, so frequently 

 associated with growth-processes that the considerations of the mo- 

 dality of cell-wall formation at the same time t)ecome considerations 

 concerning growth-types. This is also proven by the literature 

 relating to the earlier researches of Nageli, as well as by the related 

 school of evolutionary development (Kny, Leitgeb, and others). 



The following statements will explain the relation of growth to 

 cell-division. 



With Sachs we distinguish three cases. 



1. Growth without Cell-division. — This rare occurrence is met 

 with in Siphonacece, a group of marine algae. These plants are very 

 large, but have only a single piimordial utricle with various branch- 

 ings or projections ; they have a continuous apical growth, while the 

 distal end is closed by coagulated plasm. 



2. Cell-division loithout Growth. — This again is of rare occur- 

 rence. It is typically represented in the algal group Sphacelariacece. 

 A single apical cell divides with a transverse septum. This cell, 

 which is situated at the apical area of the stem, represents the grow- 

 ing part of the plant. As soon as the transverse septum has cut 

 off a posterior segment this segment ceases to grow. It, however, 

 divides into a large number of cells by the formation of numerous 

 septa. 



