218 Prof. Mohl on the Penetration of the 



membrane is said to penetrate through the stomata into the 

 spiracles, clothe their walls, and extend thence, in the leaves of 

 NcD'cissus Jonquil/a, in the form of vessels into the intercellular 

 passages. 



Payen* states that the cuticle enters the stomata and, in Cac- 

 tus pcruvianus, extends down through the layers of the epidermis 

 as a thin membrane in the form of a mutf. This membrane, 

 like the cuticle itself, is said to be coloured yellow by iodine, and 

 to exhibit the same resistance to the action of sulphuric acid. 



These statements induced me to institute some investigations 

 on the subject in question. For this purpose I adopted the 

 method of soaking the sections of the leaves for examination in 

 tincture of iodine, washing them with water, and then submit- 

 ting them to the action of sulphuric acid. This latter not only 

 heightens the yelloAV tint of the cuticle coloured by iodine, but 

 it has especially this advantage, that the cells of the epidermis of 

 most plants are disintegrated with the production of a blue coloiu'- 

 ing or entirely dissolved, according to the strength of the acid 

 employed, when the cuticle can be very readily distinguished 

 and separated from them. From these investigations this gene- 

 ral result was obtained, that, as asserted by Payen, a direct con- 

 tinuation of the cuticle penetrates into the stomata and proceeds 

 down between the porous cells to the spiracles in the form of a 

 tube very highly compressed on both sides. No doubt can be 

 entertained, on a careful examination, that this tube is not closed 

 either at the entrance into the stomata or lower down between 

 the porous cells. Arrived at the inner termination of the sto- 

 matic aperture, this tube dilates into a smaller or larger funnel- 

 shaped expansion, which clothes the inferior surface of the epi- 

 dermis so far as it closes the spiracle externally. 



Some diiFerences occur with respect to this funnel-shaped ex- 

 pansion in various plants. Generally the expansion of the funnel 

 extends only as far as true cells of the epidermis form the outer 

 wall of the spiracles ; and it is cut off short at the limit of the 

 outer wall and of the lateral walls of the spiracles formed of green 

 parenchymatous cells, so that the margin of the funnel presents 

 irregularities corresponding to the rounded-oif lateral walls of 

 the parenchymatous cells. In general no appendages penetrate 

 from the margin of the funnel into the intercellular passages 

 running beneath the epidermis and connected with the spiracles ; 

 for instance, in the stem oi Euphorbia officinarum, Cacalia Kleinia, 

 Lepisinium Myosurus, in the leaves of Agapanthus umhellatus, Nar- 

 cissus Jonquilla, Pothos lanceolata, and in the leaf-like branches 

 of Ruscics aculeatus. In other cases, on the contrary, appendages 

 proceed from the margin of the funnel-shaped expansion through 



* Menioiie sur le D^veloppement des Vegetaux. 



