1883.] Mr M. G. Potter, On the Structure of the Ice Plant 33 



M. Martinet has not however more fully investigated the nature 

 and development of these vesicles. 



The vesicles had been previously described by Mirbel 1 and 

 Guettard as Olandes utriculaires ou ampulaires, and by Schrank 

 as Schlauchdriisen. De Candolle 2 had described them as Glandes 

 utriculaires formed by a swelling of the epidermal cells and con- 

 taining a colourless alkaline fluid. They had also been roughly 

 figured by Meyen 3 and Lindley*. 



The vesicles are formed on the surface of the stem and leaves, 

 when very young. Each vesicle arises from a single epidermal 

 cell, and always remains unicellular. The epidermal cell about to 

 form a vesicle grows outwards, as seen in Figures I. and IV. a. This 

 part of the vesicle, which is first formed does not always alter its 

 form, but sometimes remains as the drawn out apex of the vesicle 

 (Fig. v.). This occurs especially on the leaves. The vesicle, 

 when young, has its base about as wide as the cells of the ground 

 tissue lying next to the epidermis, and which support it. As these 

 cells increase and divide, the vesicle grows uniformly with them, 

 and at the same time grows outwardly, forming a bladder-like 

 excrescence on the epidermis (Figs. V. and VI.) which is supported 

 by numerous cells belonging to the ground tissue and not to the 

 epidermis. They are generally elongated ia the direction of the 

 growth of the part of the plant on which they are borne, and thus 

 have their bases much longer than broad. 



The vesicles formed in the manner above described are situated 

 close to each other, are filled with a clear colourless cell sap, and so 

 cause the plant to appear covered with ice. They are separated 

 from each other by a small but varying number of epidermal cells, 

 among which lie scattered numerous stomata. The vesicles are 

 formed very early close to the growing point of ' the stem and 

 branches and the leaves, whilst still very young: as these parts 

 grow and increase in size new vesicles are formed from the young 

 cells of the epidermis. 



Thin sections of the stem or leaf-bearing vesicles stained with 

 Chlor. Zin. Iod, (Schultz solution) shew that the wall of the vesicle 

 is much thickened and composed of cellose, since it is stained 

 blue ; on the exterior of the vesicle, however, is seen a thin line of 

 cuticle stained yellow, and continuous with that covering the 

 adjacent epidermal cell. The wall of the vesicle is uniformly 

 thickened, except that part which separates the cavity of the 

 vesicle from the cavity of the cells supporting it. Here lenticular 

 spaces are left unthickened, as seen in Fig. vii., a longitudinal 



1 Elem. de Physiol. Veget. et de Bot. Paris, 1815. 



2 Organogr. Veget. i. p. 78. 



3 Ueber die Secretions-organe der Pflanzen. Berlin, 1837. 



4 Introduction to Botany, Vol. i. fig. 16 e, page 159. 



VOL. V. PT. I. 3 



