1883.] Significance of Water Glands and Nectaries. 41 



I have only dwelt very briefly on these observations, but 

 I would remark once for all that they were conducted with great 

 care. The temperature was as near as possible constant, and 

 every precaution was taken to guard against transpiration. 



2. Branches of Limoniastrum, Polypodium, and Fuchsia were 

 cut off under water and placed in a glass of water in a pan con- 

 taining the same liquid — the whole being covered with a bell-jar. 

 They were examined during the daytime and at night, and 

 careful experiments were also made in the daytime, when the 

 branches were exposed to the action of light, and when placed in 

 artificial darkness : the temperature remaining constant. The 

 difference in the amount exuded in light and in darkness was 

 indeed most striking, and especially so with regard to Limonias- 

 trum and Polypodium. 



As is well known from the observations of de Bary 1 the leaves of 

 Limoniastrum in common with so many of the Plumbaginaceae are 

 covered with small masses of chalk. These masses occupy small 

 depressions on the leaf-surface, and at the base of each depression 

 is situated a group of some eight epidermal cells, which are quite 

 unconnected with the vascular- bundle system, and, as my results 

 show, are capable of excreting by their own activity, water con- 

 taining salts in solution. The latter fact seems to me to be of 

 some interest, and especially so, since the activity of the glands is 

 very pronounced. For example, a piece of the stem of Limoni- 

 astrum was cut off and experimented upon. It was then placed 

 in a glass of water, exposed to the air. Fourteen days after, it was 

 placed a second time under the bell-jar and again exuded water 

 from its glands with great vigour. 



In Polypodium and in many of the Filicineae we know chiefly 

 from the researches of Mettenius 1 that the leaves are also covered 

 at certain areas of their surface, with little masses of chalk. 

 Mettenius observed that these masses were placed directly over 

 the endings of certain of the vascular bundles. The bundle 

 apparently came to the surface, and was covered by an epidermis 

 from which stomata were absent. Since I am not aware that 

 there is a more detailed description than the above, I have thought 

 it well to give a figure of the structure in question. See Fig. ill. 

 It will be seen that the bundle ends in a mass of tracheides, and is 

 covered by some two layers of very small cells, and finally by an 

 epidermis, with thin walls, large nuclei, and granular protoplasm. 

 Here, as in Limoniastrum, there is but little doubt that it is the 

 epidermal cells, which actively excrete the water containing -chalk 

 in solution, which, as the water evaporates, is precipitated as a thin, 



1 De Bai-y, loc. cit. p. 113. 



2 Mettenius, Filices horti Lipsiensis. 



