THE VEGETABLE CELL 281 



higher forms subsequent changes in the character of the septa 

 gi^e rise to very different appearances in tlie cells, the latter 

 showing great differences in size and degree of development. In 

 all cases, however, they arise in the manner described, by the 

 activity of the protoplasm. 



We can thus see that the living substance is the essential 

 part of the cell, and all other structures found in connection with 

 it are only subordinate to the requirements of the protoplasm. 



In the simplest forms, each pi'otoplast discharges all the vital 

 processes of the plant. As, however, complexity of the plant body 

 increases, there may be traced a division of this work, particular 

 protoplasts taking up one, others another, duty. Thus some are 



Fig. 611. 



Fvj. 611. Continuity of the protoplasm of contiguous cells of the endosperm 

 of a Palm seed (^Bentinckia). a. Contracted protoplasm of a cell. 6. A 

 group of delicate protoplasmic fibrils passing througha pitinthecell-wall. 

 (Highly magnified, after G-ardiner.) 



particularly concerned in nutrition, others in reproduction, and 

 so on. This division of labour is the clue to the differences of 

 structure and appearance which we find in different parts of 

 the plant mass, cells being modiiied in relation to the work 

 which ultimately falls to their share. Thus all differentiation 

 of structure is to be traced to division of labour. 



In the older parts of plants we find the cells consisting of the 

 wall alone, the protoplasm having disappeared. Such cells are, 

 of course, not living. 



It is most convenient to study first the vegetable cell as it 

 exists in a portion of the higher plants, such as the younger part 

 of a stem or root. If we cut a section of such a structure 

 we find the cells all alike and all presenting the following 

 features : 1. The limiting membrane or cell-wall. 2. The 



