417 



and (|uicklv. The slower and more retarded development of double blocjms 

 may be traced to greater distribution of the water and nutritive substances 

 conveyed through the petioles over a more considerable leaf area. The loss 

 in transpiration, due to the increased number of petals, is greater and can 

 in no way be replaced by supplying w ater to the roots. Consequently, the 

 organs develop more quickly ; they become ripe prematurely and cease 

 growing before the blossom has been completely developed. On this account 

 half open blossoms often fall where there is great atmospheric dryness. 

 This should not be confused with the dropping of the blossoms, due to 

 excess of water. In the latter case it may often be observed that both the 

 blossoms and peduncles fall, ^^^ith excessive transpiration in a very dry 

 atmosphere, the petals fall where they join the peduncle after having 

 turned brown there. 



AMien, as is often attempted in greenhouses, an artificially moist atmos- 

 phere is produced by abundant watering of entire plants, their condition is 

 improved only if the flpwer pots stand on the soil, since the vaporizing 

 dampness from the soil keeps the atmosphere constantly moist. But if the 

 pots stand on wood, iron or stone, the blossoms shrivel up in spite of the 

 watering and a Botrytis growth is found where the petals loosen. This 

 leads consequently to erroneous conclusions since Botrytis diseases are 

 usually accompanied by great atmospheric humidity. 



The double staminate blossoms of tuberous begonias fall in excessively 

 dry air. and form one of the most striking examples of the difficulty. I 

 observed this often in the dry summer of 1904 in places which had never 

 had direct sunlight. That the falling of the petals was actually due to dry- 

 ness of the air was shown by an experiment in which plants were used, 

 w-hich usually drop their blossoms at the time of opening. They retained 

 and developed them, however, if placed over broad basins filled with water. 



The pistillate blooms aUvays mature. The first indication that the 

 staminate blossoms are going to fall is that the bud does not straighten up 

 but remains drooping. A\'ith the hand lens a small brown ring may be seen 

 at the union of the calyx and peduncle. There the young tissue is found 

 to be deep brown, its walls and contents collapsed. At the calyx, the 

 shrivelling and tearing of the tissue forms large holes until finally the petals 

 hang only by a few shreds of tissue. In the indi\'idual petals, the vascular 

 bundles also seem deeply browned even at the places which are still not 

 discolored and apparently fresh. This drying of the base is really a pre- 

 mature end of the life cycle, since the cell contains only scanty fllakes of 

 protoplasm. Near the dead tissue there is an abnormal accumulation of 

 asymmetrically formed, separate crystals of calcium oxalate, as the final 

 residue of the organic substances consumed in respiration. 



A second kind of defective blossom development, resulting from dry- 

 ness, was observed in the Uliaceae and Amaryllideae. In these instances 

 the perianth remained stuck together at the apices. Although the rest of the 

 blossom was normally developed and colored, the tips of these perianths 



