STUDIES ON SOME EXTRANUPTIAL NECTARIES. 9 



outer wall of the epithelium ; but in the nectaries of the second 

 type it is sometimes found penetrating between the secretory cells 

 SO as to cover their longitudinal walls. When the secretory 

 epithelium has stored up plenty of nectar substance, the cuticle 

 is separated from the underlying cellulose-layer and is raised up 

 from the latter. The space thereby produced between the cuticle 

 and the cell-wall, is filled up with successive secretions of the 

 secretory epithelium so as to cause the swelling of the cuticular 

 membrane. I met with this phenomenon very often on the mi- 

 crotome section of the extrauuptial nectaries of Diospyros moris- 

 siana, Cassia occidentalis and Idesia iJolycmya. 



Under favourable external circumstances and also under the 

 one-sided osmotic pressure^^ exerted by the subglandular tissue, 

 the elasticity of the cuticle is overcome, resulting in the rupture 

 of the membrane and the extrusion of the fluid on the surface 

 of the nectary. Thus the secreting phenomenon is caused. After 

 the first ample secretion, the nectaries in most cases remain 

 inactive and produce no more nectar ; the regeneration"^ of the 

 cuticle takes place only with some species of Prunus. From the 

 fact that the cuticle is often ruptured by the force of the sec- 

 reting fluid, it must be supposed that the membrane is imperme- 

 able.^^ But there are cases^^ in which the cuticle remains uninjured 

 throughout the secreting period. 



The nectar must then be secreted through the cuticle ; in 

 other words, the latter must be j)ermeable. In fact, the cuticle 

 is thinner on the surface of the nectary (generally about 7-3 [j) 



1) Wilson. 1. c. 



2) Pfetîers. PÜanzenphysiologie. II Anfl. Bd. I, p. 265. 



3) Wilson. 1. c. 



4) Koorders. 1. c 



