MEMOIRS OF THE NEW YORK BOTANICAL GARDEN. 257 



base of the leaf and to the supply of reserve food, must also play a 

 part in the excessive growth of these organs. 



Etiolation of Petiolate Leaves of Monocotyledons with Open or 

 Reticulate Venation. — The behavior of monocotyledonous leaves 

 arising from subterranean stems or storage organs, in which an ex- 

 panded lamina was supported at the end of a distinct petiolar struc- 

 ture offered marked divergences from the reactions of leaves of the 

 preceding type. The species included in this group are Aiiiorpho- 

 ■phalliis Rivieri (p. 40), Arisacma Dracontinni, A. iriphyllimi (p. 

 50), Pcltandra Virginica (p. 144), Trilliuni erechnn (p. 182), T. 

 erythroca?'pum (p. i8i), Caladiiun (p. 85), Calla (pp. 86, 87) 

 Canna (p. 88) and Cocos micifc7'a {p- 95)- Of these Aviorphophalltis 

 offers the most striking reaction since the leaves, which normally 

 awaken upon the maturit}^ of the fruit, or shortly afterward, did not 

 begin growth during the entire twenty months the plants were con- 

 fined to the dark room. The failure to grow might have been due 

 to one of two causes. The temperature, which was about 20° to 

 22° C. during a part of the period, might have been too low, or the 

 stimulative action of light might have been necessary to awaken 

 these organs. An exact analysis of the matter might be made only 

 under the environmental conditions of the native habitat of the 

 plant. Numerous specimens of the two species of Arisaema were 

 brought under experimental conditions and, in all instances, made 

 an exaggerated growth of the petioles, while the laminar portions 

 remained in a rudimentary condition with a volume not more than 

 two or three times as great as when in the bud. The laminar tracts 

 remained variously folded, and in positions determined altogether by 

 the relative activity of the scarcely differentiated tissues. The non- 

 development in this species is very clearly not due to lack of nutri- 

 tion, since plants confined to the dark room were capable of making 

 four successive growths of leaves in as many seasons at the expense 

 of the food-material in the corms. Furthermore, the structure of the 

 petioles was not so widely divergent from the normal as in petioles 

 of dicotyledons and it seems fairly probable that the question here 

 becomes one of stimulation rather than of direct nutrition in the de- 

 velopment of the laminae. The etiolated leaves of Caladiwn and 

 Colocasia developed petioles which were much longer than the nor- 

 mal, and laminae with an extension of surface less than the normal, 

 being only partially unfolded from the rolled position of the young 



