[ 506 ] 



XXXVI. 



EXUDATION OF WATEE BY COLO C ASIA ANTIQUORUM. 



By MABGAEET G. FLOOD, BA. 



(Elates XLVIII. and XLVIIIa.) 



[COMMUNICATED BY PROFESSOR H. H. DIXON, F.R.S.] 

 Bead December 17, 1918 ; published Amul 3, 1919. 



The extreme purity of the water exuded from the leaf-tips of Colocasia 

 antiquorum appeared strong evidence in favour of regarding the water as 

 either raised or exuded by a special gland, or as raised osmotically and 

 subsequently purified by glandular action. In either case we should expect 

 to find continuous tissue interrupting the stream in which the absorption of 

 water on one side and the exudation on the other side would take place, or in 

 which a separation of the solutes from the solution would be effected. 



At the suggestion of Brofessor H. H. Dixon, these experiments were 

 carried out with the object of locating the gland or tissue responsible for 

 effecting the exudation or the filtration of the water. 



The phenomenon was first observed by Schmidt of Stettin. It was 

 brought under the notice of Duchartre (3), and in 1859 he published a memoir 

 recording his observations and giving an anatomical description of the plant. 

 He considered that the exudation was related to transpiration, and stated that 

 it is " une transpiration liquide nocturne qui remplace la transpiration gazeuse 

 ordinaire ou diurne." In 1865 Mnsset(5) recorded that the drops are 

 sometimes shot out of the pores to a considerable distance, and compared the 

 exudation with the excretory system of animals. Haberlandt (4), in his " Text- 

 Book of Bhysiologieal Plant Anatomy," states that the water is secreted by a 

 hydathode, and also that the process of secretion consists in a simple 

 filtration, the energy being provided by root-pressure or by exudation- 

 pressure in the stems and leaves as well as in the root system. 



The quantity of water produced- by each leaf is considerable, the average 

 being about 10 c.cs. per night, so that enough can be collected for testing 

 purposes. One of Duchartre's leaves produced 22'6 grammes in a single 

 night, and another gave from 108 to 120 small drops per minute. When tested 



