EPIDERMIS. 



53 



MoUugo and Rubia tinctorum have practically no air-pores on the upper side, at the 

 apex they have a group of vpater-pores. 



In Papaver orientale, somniferum, and other species, 2-3 large pores lie in a small 

 cowl-like depression on the under side of the teeth of the leaf. 



Tropaeolum majus, Lobbianum and other species have over each nerve-ending at the 

 margin of the peltate leaf one very large water-pore, near this 2-3 or 4-5 (Tr. Lob- 

 bianum) additional ones v>?hich are rather smaller (Fig. ig). I have not found the 

 pores described by Mettenius and Rosanoff on the callous middle portion of the leaf. 

 Nelumbium speciosum has a group of several pores in the last-named spot. 



Among submerged water plants we know from Borodin that in Callitriche verna one 

 large open pore lies over the end of the vascular bundle, on the upper surface of the 

 leaf. In Callitriche autumnalis there lie at the same spot on the young leaf a group of 

 3-8 open stomata ; in the mature leaf the guard-cells of these break down, so that there 

 remains a wide hole in the epidermis. In Callitriche verna also this phenomenon ap- 

 pears in the older leaf: nevertheless I found the guard-cells still intact on leaves several 

 months old. The apices of the leaves of Hippuris behave similarly to those of Callitriche 

 autumnalis (Borodin). On the segments of the young submerged leaves of Ranunculus 

 aquatilis, divaricatus, Hottonia palustris, Askenasy ' found several stomata, which die off 

 with the whole apex before the complete maturity of the leaf. It is doubtful whether 

 these belong to the category in question. 



Water-pores with a short slit are known in the case of a number of species of Crassula, 

 and Rochea and many species of Saxifraga and Ficus with depressions on their leaves. 



The leaves of the above Crassulaceae ^ have round 

 spots or depressions easily seen with the naked eye, 

 either on both surfaces (Crassula portulacea. Lam., 

 arborescens, cultrata, tetragona, lactea) or only dis- 

 tributed on the upper side (C. cordata, perforata) ; 

 or forming a row just within the margin of the leaf, 

 either on both surfaces (C. lactea, ericoides, Rochea 

 coccinea), or only on the under surface (C. lycopo- 

 dioides, L., C. spathulata), in the latter, one at the 

 base of each notch between two teeth. An ending 

 of a vascular bundle expands beneath the epidermis 

 covering the depression. Scattered between the 

 small, delicate cells of the latter lie, in most species, 

 several (s-8, in C. lactea up to 25) stomata with short 

 slits, which are smaller than the air-pores of the 

 same leaf. In C. perforata and Rochea coccinea 

 (Fig. 20, comp. also below, Chap. VIII) the whole 

 depression consists of one stoma, exceeding the air- 

 pores in size, and somewhat sunk. The air-pores 

 are present in most species in large numbers be- 

 tween the large cells of the epidermis of both sur- 

 faces of the leaf. In C. cordata they are absent from 

 the upper side, which alone bears depressions. 



The leaves of the Saxifrages of the division Euaizonia have depressions on the notches 

 of their margin, those of the division Kabschia (Engler) and Porphyrion on their upper 

 side. In these depressions lime is excreted always, or at least while the leaf is young. 

 The base of these, towards which an end of a vascular bundle runs, is constructed simi- 

 larly to the spots in Crassula, delicate and small-celled epidermis with two (S. crustata), 

 or 2-4 (S. Aizoon, longifolia, Rocheliana) large stomata, or one large stoma (S. retusa, 

 oppositifolia, csesia) forming the base of the depression. 



Fig. 20. — Rochea coccinea ; small piece of 

 epidermis from margin of leaf. 5 water-pore ; 

 J air-pore, with subsidiary cells. The scat- 

 tered spots are wart-like outgrowths of the 

 outer wall. 



' Botan. Zeitg. 1870, p. 235. 



Magnus, I.e. 



