194 PLANT PHYSIOLOGY 



Pflanzen," by Dr. Alfred Burgerstein (Jena, 1904), a type of 

 work of which we need many more. On the energy relations of 

 Transpiration, the most important work is by Brown, described in 

 two papers, in Nature, 60, 1899, 479, in Proceedings of the Royal 

 Society, 76, 1905, 29 (review in Botanisches Centralblatt), and in 

 Nature, 71, 1905, 522. Transpiration being bound up with Trans- 

 port, there is important matter in Dixon's papers cited under that 

 subject earlier. Important new papers are Livingston's "The Rela- 

 tion of Desert Plants to Soil Moisture and to Evaporation," Carnegie 

 Institution, 1906, and Lloyd's "The Physiology of Stomata," Car- 

 negie Institution, 1908. 



(b) Guttation. 



The multiformity of conditions of transpiration will sooner 

 or later suggest to the student the query whether water is ever 

 eliminated by the plant in other than vapor form. Casting 

 about for evidence upon the subject from experience, he will 

 recall the familiar garden phenomenon shown by leaves of Canna 

 and some other garden plants on cool spring evenings following 

 hot days, when these plants show streams of water flowing down 

 the leaves. Recalling now the conditions under which this occurs, 

 it is evident that it accompanies a transition from highly favor- 

 able to unfavorable conditions of transpiration. The matter 

 may be experimentally tested, involving the following problem: 



Is liquid water released by young plants when favorable are 

 followed by unfavorable transpiration conditions? 



Experiment. Select a young Tropccolum, (Garden Nasturtium) 

 or a pot of young Oats (or other grass plants), and supply for two or 

 three hours the best conditions for transpiration, that is, warmth 

 bright light, and ample water. Then suddenly give the reverse of 

 these conditions, which is conveniently done by covering with a dark- 

 ened bell jar over which a stream of cold water may advantageously 

 be run. Observe any new appearances of the leaves. 



The student should now inform himself as to the extent and 

 activity of guttation in plants, its relation to much of the "dew" 

 of our native plants, the function of hydathodes, and the exact 

 physical conditions and significance to the plant of the process. 

 Also he should consider the relation of the formation of ice crys- 

 tals in the "Ice Plants." 



