1017 



from the subsidiary cells of (lie stomata, and llial liiially (he subsi- 

 diary cells (baw water from (lie guard-eells. 



The chai'acteristic pecubarity of the stomala in question seems to 

 me to consist in : 1. That the guard-cells have only a small free 

 surface, the wall of which is fairly strongly cuticularised and 2. that 

 they adjoin no epidermal cells other (haii the subsidiary cells so (hat 

 the influx and efflux of water in the guard-cells is brought about 

 entirel}' through the medium of the subsidiary cells. 



When indeed turgor decreases in the subsidiary cells before it does 

 in the guard cells there must therefore, when the plant begins to 

 wither, be a widening of the central slit of the stomata. In this first 

 stage when turgor in the subsidiary cells is already diminished, but 

 is still unchanged in the guard-cells, the subsidiary cells tend to 

 constrict the outer slit, the guard-cells tend to widen it. 



When, at a later stage, turgor has also decreased in the guard- 

 cells, the subsidiary- and guard-cells cooperate to cause the outer 

 slit to contract and then the central slit also contracts. 



In my investigation of the structure of the stomata of Rhipsalis 

 Cassiitha I had only at my disposal material from a hot-house, since 

 I had omitted to bring from Brazil spirit material of this plant 



The stomata are here, just as in Loranthaceae mostly arranged 

 transversely to the long axis ^) of the stem. 



A median longitudinal section through the stem shows that, as in 

 Viscum album, the subsidiary cells surround the guard-cells above 

 and below. Fig. 10 represents such a section perpendicular to the 

 direction of the slit and approximately through the middle of a stoma 

 of Ehipsalis Cassytha. 



In a transverse section through the stem, longitudinal sections of 

 the stoma can be obtained as iji Fig. 14 in which the bulging lower 

 part of the subsidiary cell can be seen under the dumb-bell-shaped 

 guard-cell and above the latter, in the background, the fold in 

 the wall of the subsidiary cell, which fold can be recognised in 

 Fig. 10 and projects above the level of the other epidermal cells. 



A section which, parallel to the surface, passes through the plane 

 of the outer slit above the guard-cells without touching them, is 

 given in Fig. 12. The two folds of the cell-wall are seen and between 

 them the narrow outer slit which is bounded at either end by a 

 small curved foH which is not always equally distinct. 



ij This peculiar orientation is somewhat rare. Low found it in Casuarina, 

 Pfitzer, inter alia, in CoUetia, the present writer observed it also in Cassytha 

 filiformis. 



