914 RECORD OF CURRENT RESEARCHES RELATING TO 



for the elimination of drops of water. He has studied their structure 

 and function in detail, following the observations of Borodin, de Bary, 

 and others. 



Water-pores are not always to be distinguished by their appearance 

 from ordinary stomata, but may frequently be known by being larger 

 and remaining open when the normal stomata are closed. They have 

 been long known to exist in many plants, as, for instance, many species 

 of fern, water-plants like Callitriche verna and autumnalis, Hippuris 

 vulgaris, and Banunculus aqiiatilis, and succulent plants like Golocasia, 

 Crassula, &c. By some authors they have been treated as organs of 

 secretion. They are either solitary or arranged in groups, and are 

 most common on the upper side of the leaf. In Crassula lactea small 

 depressions are visible to the naked eye near the margin of the leaf, 

 which the Microscope reveals to be groups of from twenty-five to thirty 

 of these water-pores, covered by a very thin transparent parenchyma. 

 They are distinguished from the ordinary stomata by being rounder, 

 with a nearly circular opening, and by the guard-cells being destitute 

 of chlorophyll. An actual excretion of water was not observed in 

 these — as was the case afeo in many other instances — and is probably 

 only a temporary function of them. Very similar structures occur in 

 several species of Crassula, and others belonging to the same natural 

 order. 1 he leaves of Primula Sinensis exude a large amount of water, 

 which the author believes to escape through two large water-pores 

 which he found on the lower side of each tooth. The excreted water 

 yielded carbonate of lime on evaporation. Colocasia antiquorum has 

 long been known for the remarkably copious exudation of water from 

 its leaves. Langer found on the upper side of the leaf, near the apex, 

 three gigantic water-pores, through which the elimination appears to 

 take place, with wide-open crevices. The remainder of the stomata 

 on the upper side of the leaf were much smaller, but also wide open. 

 Similar pores were observed on the leaf-stalk, w^here also an exudation 

 of water takes place. After being placed for fifteen hours in the dark 

 the large water-pores still remained wide open, while the smaller 

 stomata were more or less completely closed. 



The observation of these and many other examples led the author 

 to the conclusion that the two functions of the diffusion of gases and 

 the elimination of water are not sharply differentiated in the stomata, 

 but that an ordinary stoma may, at certain times and under certain 

 conditions, become converted into a water-pore, its guard-cells losing 

 their contractile property, and the fissure usually becoming more 

 circular. 



Respiration of Plants.* — M. H. Moissan has undertaken a careful 

 series of experiments for the purpose of determining afresh the rela- 

 tion between the volume of oxygen absorbed by plants and that of 

 carbonic acid emitted in respiration. The observations were made by 

 means of carefully constructed apparatus, on a considerable number of 

 trees, shrubs, and herbaceous plants, and with the following results : — 



Every living organ absorbs oxygen from the air, and disengages 



* 'Ann. Sci. Nat. (Bot.),' vii. (1870) p. 292. 



