1883.] Significance of Water Glands and Nectaries. 49 



secretion is due to the fact that the secreting cells " absorb water 

 (containing substances in solution) with great force on one side 

 and exude it on the other 1 ", and this solely by their own living 

 activity. The grand period of such activity may be and probably 

 is of short duration, and the further exudation of nectar may be 

 occasioned in the way that Wilson has pointed out, viz. by simple 

 osmosis. In such cells as those of Limoniastrum, on the other 

 hand, this grand period of activity is, as I have shown, of long 

 duration. 



It will be observed that I have spoken of the excretion of salts 

 of calcium and the secretion of nectar. I did so on the ground 

 that an excretion is a substance which is of no further use to the 

 organism, whereas from the fact that the nectar contains sugar, 

 and as first remarked by Bravais, and confirmed by Bonnier and 

 Wilson, is frequently reabsorbed into the tissue, there seems but 

 little doubt that the sugar of nectar can be used up in the vegetable 

 metabolism, and must therefore be regarded as a secretion. 



The view as to the use of nectar in the plant economy is, that 

 it is for the purpose of protection in the case of certain of the 

 extra-floral nectaries, and to insure fertilisation by attracting 

 insects, as in the nectaries of flowers, and also in the extra-floral 

 structures, such as those of Marcgravia. It must be confessed, 

 however, that at present we cannot give an entirely satisfactory 

 account of the part played by nectar in the plant economy, and 

 this is especially true as regards extra-floral nectaries. 



In concluding, I beg to express my thanks to Mr R. I. Lynch, 

 the able curator of the University Botanic Gardens. He- has 

 repeatedly made for me valuable observations, and many of the 

 experiments with regard to the effect of light upon the exudation 

 of water were made for me by him, and always with great success. 

 His observations with regard to the occurrence of nectaries in the 

 sepal and in the fruit are both new, and of great interest. 



Explanation of figures illustrating Mr Gardiner's paper "On the 

 Physiological Significance of Water-glands and Nectaries." 



Fig. I. Longitudinal section through a fully-developed gland of 

 Saxifraga crustata (after Gardiner). 



w — water stoma. 



e — epithem tissue. 



t = traclieide tissue. 



v = vascular bundle. 



h = hairs to catch the deposited calcic carbonate and prevent it from 

 stopping up the water pore. 



1 Sachs, Text-Book, p. 688. 

 VOL. V. PT. I. 4 



