1883.] . Mr W. Gardiner, On Water Glands, Sc. 35 



(4) On the Physiological Significance of Water Glands and 

 Nectaries. By Walter Gardiner, B.A., Clare College. 



Although the fact of the exudation of water and of nectar by 

 various specialised parts of plants has been long known, the nume- 

 rous observations which extend over a great number of years, deal 

 more especially with the structural details of such organs, and, 

 speaking generally, have not for their object the consideration of 

 the physiological significance of the organs in question. 



In the present paper I propose to briefly consider what, from 

 the already existing literature and my own observations, would 

 appear to be the physiological bearing of water-glands and nectaries 

 in the general economy of the plant. 



Water-glands. 



It is to Unger 1 , de Bary 2 , and more recently to Volkens 3 that 

 we are especially indebted, not only for their own valuable obser- 

 vations but also for their clear summaries of what has been made 

 out by foregoing investigators as to the structure of water-glands, 

 and a survey of the literature connected with the subject will be 

 sufficient to show that our knowledge of the structural details of 

 such organs is at the present time fairly complete. 



Water-glands usually occur on the margins or at the apices of 

 leaves though in some cases, e.g. species of Crassula, Ficus and 

 Urtica, they may be distributed over the upper leaf surface. In 

 structure, what is usually known as a typical gland consists of a 

 mass of modified parenchyma cells (to which de Bary 4 gives the 

 name of epithem cells), which abut immediately on the end of a 

 vascular bundle; are covered externally by an epidermis; and are 

 placed in communication with the exterior by means of one or 

 more water-pores or water-stoma. The epithem tissue is usually 

 distinguished by the clear hyaline character of its cells; by the 

 abundance of protoplasm in them; and by the .absence from their 

 structure of chlorophyll grains. The vessels of the vascular 

 bundles do not, as Volkens 5 has represented, end blindly at the 

 epithem tissue, but between the two forms of tissue are interposed 

 numerous tracheides, so that there is always a gradual transition 

 from the one form to the other, and when studied from a 

 developmental point of view 6 we see quite clearly how this 

 transition occurs. 



1 Unger, Beitr'dge zur Phijsiologie der Pjianzen. 



2 De Bary, Vergl. Anatomie, p. 55 et seq. and 390 et seq. 



3 Volkens, Jahrb. K. Bot. Gartens. Berlin, 1883. 



4 De Bary, loc. cit. p. 391. 



8 Volkens, loc. cit., see Figs, of Plates IV. V. and VI. 

 6 Gardiner, Quart. Journ. Mic. Sci. Vol. xxi. N.S. 



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