526 EXPERIMENT STATION RECORD. 



modifications to regulate transpiration. The investigations were carried on to 

 determine the alleged regulation of water loss bj' the stomata and the physio- 

 logical causes of stomatal movement. 



On the theory of stomatal regulation of water loss, a close correlation would 

 be expected between the daily periodicities of transpiration and of stomatal 

 movement. The rate of transpiration, however, was found to increase for a 

 considerable period after the maximum stomatal opening had been reached. 

 The diminution in the rate of transpiration during the latter part of the day 

 may be interrupted by intervals of increase without any interruption in the 

 diminution of stomatal dimensions. Such conclusions throw doubt on the accu- 

 racy of the view of stomatal regulation as suggested above. 



It was found that the rate of transpiration may undergo sudden and wide 

 changes without the accompaniment of a sufficient change in the dimensions of 

 the stomata to account for them on this theory. It appears that stomatal 

 regulation of transpiration does not occur, although conservation of the con- 

 tained water follows the complete closure of the stomata. 



Observations on the changes in the rate of transpiration during constant con- 

 ditions of temperature and relative humidity, and in total darkness, brought 

 out the fact that there exists in Fouquieria an induced rhythm in transpi- 

 ration, the cause for which is quite obscure. 



During the process of wilting there was found to ensue a gradual closure of 

 the stomata without any preliminary opening such as is claimed to occur by 

 Francis Darwin. The beginning of closure occurs somewhat later than initial 

 wilting and seems to be a result of water loss by the leaf as a whole. 



In studying the physiology of guard cells, the author found in the Verbena 

 a fluctuation of the amount of starch within the plastids of the guard cells, 

 accompanied by a complementary fluctuation of the oil content. The presence 

 of the oil and the conditions of its formation indicate that it is of secondary 

 Importance. The starch content was found to be at its minimum during the 

 later hours of the morning. During the earlier hours of the morning the 

 starch is dissolved and disappears from the plastids of the guard cells, to reap- 

 pear and Increase to the maximum toward the afternoon and earlier part of 

 the night. The movements and periods of stasis of the stomata are closely cor- 

 related with this appearance and disappearance of starch. The author states 

 that it would appear that the plastids of the stoma, which present certain 

 morphological differences needing further investigation, normally accumulate 

 starch when exposed to the blue end of the spectrum, to darkness, and to air 

 devoid of carbon dioxid. This is contrary to the conditions under which starch 

 is ordinarily formed in the chlorenchyma. Beginning with an initial condition 

 of the entire absence of starch, this substance was found to be formed and to 

 materially increase when photosynthesis was impossible. It seems that the 

 guard-cell plastids are not only able to accumulate starch in the dark without 

 a supply of carbon dioxid, but normally do so by drawing upon the general sup- 

 ply of the leaf. The disappeai-ance of starch from the guard cells in the early 

 morning, and its persistence in darkness, especially in plants in which a supply 

 of food materials is available, compels the assumption of a mechanism of diges- 

 tion of a different kind from the ordinary diastase of the leaf, and while such 

 an agent has not been demonstrated, its probable occurrence has been reported. 

 It is believed that a clear understanding of this assumed ferment will account 

 for the movements of stomata which have remained unexplained by the gener- 

 ally prevalent photosynthetic theory. 



The relation of stomatal activity to normal, though high, temperatures and 

 to the very low humidities of the desert appears to be the same as to these 

 conditions anywhere, and there seems to be no adaptive behavior particulacly 



