276 



LEAVES 



adjacent compartments are usually so closely joined that the 

 compartments appear separated by a single solid partition, and 

 thus the numerous compartments, solidly joined, constitute a 

 plant body with sufficient rigidity to maintain a definite shape. 

 Through very small pores in the cell walls the protoplasts are 

 commonly connected by small protoplasmic strands and thereby 

 the protoplasts of neighboring cells communicate. (Fig. 248). 

 Cellulose is represented by the formula (C 6 H 10 O 5 )n, the n 

 standing for an unknown number of the combinations C 6 H 10 O 5 . 

 It is readily seen that C 6 H 10 O 5 is a molecule of the photosynthetic 



sugar with a molecule of 

 water dropped (C 6 H 12 O/^ 

 H 2 O=C 6 H 10 O 5 ), and that a 

 molecule of cellulose (C 6 H 10 

 O 5 )n consists of an unknown 

 number of molecules of sugar 

 with a molecule of water 

 dropped from each in form- 

 ing the chemical combina- 

 tion. 



Cellulose, due to its elas 

 ticity and to its permeability 

 to water and solutions of 

 food, is suitable material for 

 the cell walls. It permits 

 stretching during growth and 

 does not obstruct the en- 

 trance of water and solutions 

 of food to the protoplasts. 



FIG. 248. Cells with protoplasm 

 shrunken, so that the fine strands of 

 protoplasm extending through the ^cell 

 walls and connecting neighboring pro- 

 toplasts may be seen. Highly magnified. 



When cellulose walls are chiefly for strength, as in the case of bast 

 fibers, then cellulose is added until the walls are much thickened. 

 In many places cell walls need other substances in addition to 

 cellulose to best adapt them to their function, consequently other 

 substances, such as lignin, cutin, and suberin, are often formed 

 from the photosynthetic sugar and combined with the cellulose. 

 Lignin combined with cellulose forms ligno-cellulose which we 

 commonly know as wood. Wood is especially fitted to give 

 strength and serves this purpose in trunks of trees, shrubs, and 

 is present to a less extent in herbaceous plants. In the coats of 

 some seeds and in the shells of nuts wood is present. When the 



