290 



TEXTBOOK OF PLANT PHYSIOLOGY 



**V, 



the inflorescence have completed their embryonic development, 

 then meristematic growth commences and a rapid elongation of 

 the internodes sets in. At this period the inflorescence comes out 

 of the tubelike leaf sheaths which till then have tightly enclosed 

 it (Fig. 112). 



In some cereals, these two stages are separated by the winter 

 period, when growth completely ceases and the plant enters into a 

 state of rest. This condition may be of various intensity and 



duration. It may involve the 

 whole plant or only parts of 

 it. The best investigations 

 have been made on the dor- 

 mancy of buds and branches 

 of trees. In early summer, 

 soon after the shoots and 

 young leaves have expanded, 

 new buds arise in their axils. 

 They gradually increase in 

 size during the summer 

 months, passing through the 

 stage of meristematic growth. 

 Towards the end of the grow- 

 ing season, all parts composing 

 the next year's shoot may be 

 distinguished already in the 

 buds. Frequently, even the 

 whole flower cluster is present. 

 But in this period meriste- 

 matic growth is not followed by 

 elongation. During the fall and winter these buds are in a state 

 of rest. 



One must not imagine that in this state there is a complete 

 cessation of all vital processes. Respiration continues in all 

 resting organs. The transformation of reserve substances also 

 takes place. In the twigs and buds of trees, for instance, starch 

 usually disappears during the winter and in its place sugar and 

 sometimes fat accumulate. Toward spring reverse metabolic 

 changes may be observed. In general, all vital activities manifest 

 themselves during dormancy with the exception of growth, which 

 does not take place, though the external conditions may be quite 



Fig. 112.- 



-Terminal bud of a young maize 

 plant. 



