38 Mr W. Gardiner, On the Physiological [Nov. 12, 



deal with certain of my own results, which have some bearing on 

 the question. 



With regard to the glands of Monocotyledons and Dicotyledons, 

 Volkens seeks in certain instances to trace a definite epithem 

 tissue, e.g. in Calla and Alisma. As he rightly states, there are 

 certain layers of cells which are marked off from the rest, both on 

 account of their cell-contents and on account of their small and 

 old-looking nuclei, as opposed to the large and well-developed 

 nuclei of the neighbouring parenchyma cells, but it would seem 

 that too much stress should not be laid upon this distinction, in con- 

 sequence of the greater and more striking fact, that, stated gene- 

 rally, in the typical Dicotyledonous gland there is always a well- 

 developed and very conspicuous epithem, whereas in Monocoty- 

 ledons, this epithem is inconspicuous and is only recognised with 

 difficulty. Thus in the case of Richardia Africana one is led to 

 believe that the whole of the narrow projecting process of the leaf 

 apex should be regarded as an organ for the exudation of water, 

 and tbat in this organ, there is not that differentiation as in Dicoty- 

 ledons, but only a number of well-developed water-stomata, and a 

 vascular bundle which is surrounded by a few layers of practically 

 undifferentiated parenchyma cells. 



It seems an important omission on the part of Volkens 1 to leave 

 out of his figures the tracheides, in which in all cases the vascular 

 bundles end, for by so doing, his figure of Alisma, for instance, gives 

 one the idea that the vessels of the vascular bundle end blindly, 

 immediately beneath the epidermis, and that in older leaves, owing 

 to the rupture of the latter tissue, the vessels open freely towards 

 the free surface. In reality however the arrangement is like that 

 of Sagittaria, which I have attempted to represent in Fig. n„ and 

 on rupture it is the tracheides which are exposed. 



The water-glands and their stomata appear at a very early age 

 in the development of the leaf. As I showed in Saxifraga crus- 

 tata 2 , the development of the leaf as a whole and of each leaf 

 segment, is first apical and then basal. The differentiation of the 

 young tissue into a vascular bundle and an epithem tissue rapidly 

 proceeds, and unites the young water-gland to the general vascular- 

 bundle system of the stem, and the whole gland is developed and 

 in action before the appearance of a single ordinary stoma of the 

 leaf. 



As to the physiology I worked with care over Sach's results, 

 and over certain of those of Moll. I say certain, since I preferred 

 not to use artificial pressure, but to study the phenomena as in- 

 duced by the normal pressure of the root, under varying external 

 conditions. 



1 Volkens, loc. cit. 2 Gardiner, loc. cit. 



