BOTANICAL TERMS. 



A-Ssimilation. 



This is the process, by which the carbon obtained from carbon 

 dioxide is corabined with the elements of water to form 

 starch. 



Metastasis. 



This is the process bj' which the starch, resulting from 

 assimilation, is converted into soluble forms and removed 

 from the cells where it was produced to other portions of 

 the plant where it is needed for purposes of growth, or. if 

 there is an excess, to storehouses such as roots, bulbs, 

 etc. , for future use. 



Circumstances Affecting Growth. 



Temperature. — Growth may be stopped altogether hy either 

 too low or too high a temperatare, and between the lim- 

 its within which any given plant is found to be capable 

 of growth there will be found a particular degree of 

 temperatitre more favourable to growth than any other, 

 either above it or below it. This may be called the opti- 

 mum. The effect of temperatitx-e differs considerably ac- 

 cording to the amount of water present in the part 

 affected, dry seeds, for instance, resisting a temperature, 

 either high or low, to which soaked seeds would at once 

 succumb. 



Light. — Light is essential to assimilation, but seeds and 

 tubers, as well as many of the lower plants which are 

 without chlorophyll, such as Mushrooms, will grow in 

 the absence of light as long as the stock of assimilated 

 material tipon which they draw is not exhausted. The 

 growth which takes place in the cambium-layer of dico- 

 tyledons and in roots is another example of increase in 

 size in the absence of light. The assimilated material in 

 all these cases, however, has been previovisly elaborated 

 elsewhere. 



Light is found to exercise a retarding inflitence upon 

 growth. A plant, for instance, in a window will bend 

 towards the light, because the cells on the side nearest 

 the window grow more slowly than those which are 

 shaded, thus causing curvature of the stem and petioles. 



Gravitation. — Gravitation also affects growth, as we know 

 that the stem and root, or axis of the plant, are usually 

 in the line of the radiiis of the earth at the place of 

 growth. If a seedling plantlet be laid with the stem and 

 root horizontal, the stem will curve upward and the root 

 downward in the endeavour to restore the vertical direc- 

 tion. 



Historical Goiiection 



