REPRODUCTION AND DISPERSAL 889 



winter there is a gradual increase of available food in the embryonic 

 organs; probably this relative absence of available food is one of the chief 

 reasons why autumnal buds open so tardily or remain closed, when they 

 are exposed to favorable temperatures. 



It is probable that buds undergo progressive changes other than those 

 related to the food supply, though the nature of such changes is unknown. 

 Recently it has been shown that the development of buds can be greatly 

 stimulated by various methods of treatment during the early part of the 

 resting period. For example, the subjection of resting buds to anes- 

 thetics, to freezing temperatures, to warm water baths, or to various 

 methods of chemical treatment, results in a material shortening of the 

 rest period, provided the plants are brought subsequently into conditions 

 suitable for bud development; as might be expected, this artificial 

 hastening of development has proven to be of great commercial advan- 

 tage in the " forcing " of bulbs, and of lilacs and other ornamental 

 shrubs. The exact effect of these methods is unknown, although it is 

 believed that the stimulation of development in potato tubers that have 

 been subjected to low temperatures is due to the fact that at such 

 temperatures there is a rapid accumulation of diastase, which results 

 in the transformation of starch into sugar, and also to the probability 

 that the cell membranes are more permeable than at higher tem- 

 peratures. 



Flowering periods in arid and in frigid climates. — In uniform trop- 

 ical climates, the flowering of plants does not characterize any one season 

 more than another, many species even being everbloomers. In most tem- 

 perate climates, flowers appear at all seasons that are in any way favor- 

 able; estival flowering occurs chiefly at the expense of food accumulated 

 in spring, but the earlier vernal flowers utilize the food accumulated 

 during the previous vegetative period. In respect to anthesis, arid and 

 frigid climates present certain features of marked contrast to temperate 

 climates and to uniform tropical climates. In arid climates the incep- 

 tion of the rainy period is marked by vegetative activity, but this is 

 checked at the beginning of the next dry period. Flowering, however, 

 is to a large extent associated with the dry period; indeed, in many cases, 

 anthesis is as definitely associated with the dry season as is vegetative 

 activity with the rainy season. In the monsoon district of eastern Java, 

 where the year is about equally divided into two periods, one of con- 

 siderable rain and the other of drought, more than 60 per cent of the 

 species bloom solely in the dry period, while only 8 per cent bloom 



