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exuded out through the pores, of which there are in this case a 

 considerable number to each gland, so that the amount of water 

 poured out in this way by a plant may be considerable. During 

 the day this process will cease, because the amount of transpir- 

 ation is so great that it soon empties the vessels, and keeps them 

 in that condition. That these drops are not drops of dew, as 

 might be at first supposed, may be proved by placing a bell-jar 

 cover over the plant, when we will find that the process still goes 

 on, and consequently the water must be poured out from some 

 part of the leaves themselves. This secretion of water de- 

 pends on the evident root pressure, since it only takes place 

 when we have fluid in the vessels, and will not take place 

 when the leaf is cut off from the plant unless we replace the 

 root pressure by forcing in water under the pressure of a column 

 of mercury. According to Dr. S. H. Vines, and Dr. Moll, of 

 Amsterdam, possibly some definite correlation exists between 

 the presence of excretory organs such as water-pores, and the 

 existence of evident root pressure in a plant. Hofmeister (Flora, 

 1862) could detect no root pressure in Conifers, where the vessels 

 are few, the only ones being those first formed, which soon die ; 

 and Moll has failed to discover any excretory organs in their 

 leaves. 



In by far the larger number of plants, the activity and life of 

 the water gland and structures analogous to it appear to be 

 co-existent with that of the leaf as a whole. In certain cases, 

 however — e.g., species of Musa, Richardia, and the grasses, in 

 which the gland is borne at the apex of the leaf— the apex soon 

 withers, and the gland becomes destroyed. Thus, in very 

 young barley plants {Hordeum vulgare), large drops of water 

 may be seen hanging on the apex of each leaf, even though the 

 temperature of the surrounding air be as high as 74 Fahr. 

 As they grow older the secretion stops, and later each leaf 

 apex withers up and dies. Another case of secretion or excretion 

 of a very different nature is that of honey (which is a solution 

 of sugar in water), by flowers. In this case the secretion or 

 pouring out of water will take place for days just as well after 

 we have cut off the flower from the stem and placed it in water 



