Ways in Which Plants Increase in Size 337 



barometer, should theoretically have some slight effect, but 

 hardly any is appreciable in practice. 



If now, we return to the graph of growth (figure 123) and pro- 

 ceed to eliminate those fluctuations which are traceable to tem- 

 perature, light, and moisture, there still remains one peculiarity 

 of much consequence, viz., a gradual rise in the graph as a whole, 

 followed by a more abrupt descent. This means that the flower- 

 stalk of the Grape Hyacinth, even when all disturbing external 

 factors are eliminated, does not by any means grow at a uniform 

 rate from start to finish, as one might naturally suppose, but, after 

 beginning, grows faster and faster up to a point of highest rate, 

 beyond which its growth is slower and slower until it stops. This 

 peculiarity of growth, however, is not confined to the flower-stalk 

 of this plant, but is very wide spread; and it has even a name of 

 its own, viz., the " grand period." Thus, it is characteristic of 

 winter buds; and this explains a phenomenon in connection with 

 their opening which most people must have noticed, viz., that 

 buds swell very slowly at first in the spring, seeming to take an 

 interminable tune before they show their green leaves, after 

 which they open out very quickly, almost over night as it seems, 

 to nearly the full size of their parts; and then they complete their 

 final growth rather slowly. This opening takes place on the crest 

 of the grand period as a rule, although it is complicated of course 

 more or less by the effects of temperature. Leaves, single flowers, 

 germinating embryos, fruits, and a good many other parts display 

 the grand period. It is not, however, universal; for some struc- 

 tures, like stems which continue their growth all summer, pursue 

 an even course affected only by varying temperature, moisture, 

 or light. 



By suitable modifications in details, records may also be se- 

 cured by the auxograph for the growth of leaves and of roots. 

 The graphs in general are very similar to those obtained from 

 stems. But there is one feature of the growth of leaves, stems and 

 roots, about which the auxograph gives no information, namely, 



