56 PLANT GROWTH 



baceous plants, continue to elongate during most of their 

 period of life. 



Growth in thickness of woody plants is most rapid also 

 in the spring but it continues all summer at a slower and 

 slower rate. The difference in the growth rate in late sum- 

 mer and the following spring can be seen by the much larger 

 spring cells, which make the yearly rings so conspicuous in 

 cross sections of wood. They are equally clear as long 

 streaks in oak flooring and in much of the wood of our furni- 

 ture. The limited summer growth enables the plants to store 

 food for the early growth of the following year. 



Buds appear on new wood at the axils of the leaves about 

 the time the leaves appear. Buds which are clearly evident 

 on the above twig C will continue to grow larger through the 

 summer as is shown on twig D. 



Some buds, called dormant buds, do not grow at the nor- 

 mal time after their formation (leaf buds 3 and 4, Fig. 13). 

 Dormant buds act as reserve buds and they will grow if those 

 higher on the branch are destroyed, as may happen by freez- 

 ing or by pruning, even after a dormancy of one to several 

 years. All buds that grow at their normal period are called 

 active buds. 



Buds are of three kinds according to their contents: Fig- 

 ure 13 shows two kinds, leaf buds and flower buds. Leaf 

 buds contain several embryo leaves with very small unde- 

 veloped buds, and a very small branch. The flower buds 

 usually have only embryo flower parts. The third type, 

 called mixed buds, contains both leaves and flowers. In 

 many cases the kind of bud can be determined with a micro- 

 scope as early as July before they open the following spring. 

 Most flower buds of trees can be seen during the winter with- 

 out magnification. The experienced fruit grower can recog- 

 nize them by their shape. Since the flower buds begin their 

 development so many months, almost a year before they 

 open, it is clear that cultural treatment to regulate flowering 



