154 A TEXTBOOK OF BOTANY [Cn. IV, 7 



water from the stem, swell and open, and the leaves and 

 flowers push forth and rapidly enlarge to their full size, 

 as the familiar Horse Chestnut so strikingly illustrates. 

 The microscope shows that this expansion is chiefly effected 

 by a great increase in the size of the previously-formed 

 cells, of which the large cavities are now empty of food, but 

 tensely filled with water. That this enlargement is really 

 brought about by absorption of water is very well proven by 

 the fact that many such greatly-enlarged parts if thoroughly 

 dried in an oven are found to be no heavier than in the 

 original buds. This is especially clear in embryos, which, 

 often germinating to a size a dozen or more times that which 

 they had in the seed, actually lose dry weight in the process. 

 The functional reason for 'this rapid spread of a little dry 

 substance upon a great deal of water is plain ; the plant mode 

 of life requires a spread of green surface as early as possible. 

 Third, the enlargement nearing completion, the parts mature, 

 acquiring the final details of their coloration, thickening, and 

 other features connected with the more effective performance 

 of their functions. In this state they continue until their 

 function is completed, after which they die and vanish 

 through decay. 



The development, or formation (as distinct from enlarge- 

 ment), of new parts takes place in meristematic cells (Figs. 

 92, 162), which divide more rapidly in some places and direc- 

 tions than in others. These divisions are apparently effected 

 by the cytoplasm of the cells, which is controlled in the pro- 

 cess by the chromosomes of the nuclei, as will appear more 

 fully in connection with reproduction. 



We turn now to enlargement, the most striking and familiar 

 phase of growth. So rapidly does it proceed in the stems of 

 some plants out of doors in spring that its progress is visible 

 from day to day. It is said that the growth of Bamboo in 

 the tropics is so rapid as to be directly perceptible at times to 

 the unaided eye, reaching often to more than two feet within 

 twenty-four hours. Ordinarily, however, growth proceeds 



