48 Rennert : Seeds and Seedlings of Arisaema 



The functional plumules of A. Dracontiuvi exhibit a tendency 

 toward degeneration. A comparison of the plumules of the two 

 species will well demonstrate the particular instances. The fully- 

 grown leaves of A. triphyllum are ovate, the largest being T)^ mm. 

 in length and 30 mm. in width, while the smaller are 25 mm. 

 by 13 mm. The functional leaves of A. Dracontium vary greatly 

 in the shape and size of the lamina and in the length of the petiole. 

 In outline they range from broadly elliptical to nearly circular and 

 all bear a mucronate point at the tip as does A. tripliylliim. The 

 largest leaves of ^. Dracontium are about 25 mm. in length by 22 

 mm. in width, but the greater number are smaller, some being 

 only 6 mm. by 3 mm. The margin of nearly all leaves of A. tri- 

 phyllnvi are very finely serrulate ; while some leaves of A. Dracon- 

 titini display a tendency to serrulation, more often they are entire. 

 The upper surface of the A. triphyllum leaf is covered with faint 

 whitish lines ; this appearance is due to the presence of elongated 

 raphide cells in the mesophyll directly beneath the epidermis. A. 

 Dracontium has numerous raphide cells in the mesophyll but they 

 are not so large as those of A. triphylbim and cannot be distin- 

 guished without the aid of the microscope. The under surface of 

 the leaves of A. triphylhiin is covered with a waxy bloom and the 

 upper surface also shows some wax. In A. Dracontium the wax is 

 very much thinner on the under surface and barely discernible on 

 the upper. As a consequence the leaf oi A. Dracontium wilts very 

 quickly after being removed from the plant. The development of 

 stomata on both leaves is about the same. The leaves of both 

 species are pinnately net- veined. In A. triphyllum one pair of the 

 lateral branches is more strongly marked than the others, fore- 

 shadowing distinctly the plan of the mature trifoliolate leaf. In A. 

 Dracontium the plan of venation is more generalized. The lateral 

 veins have all equal value and are neither so well marked as some 

 nor so faint as other lateral veins of the leaf of A. triphyllum. 

 The mesophyll of the A. Dracontium leaf is not so well developed 

 nor so well supplied with chlorophyll as is that of A. triphyllum. 

 Those plumules of A. Dracontium which become assimilatory 

 organs are functional for a shorter period than those of A. triphyl- 

 lum, for they wither upon the plant much sooner. Tho.se of long- 

 est duration last not more than three months while some send up 



