TRIPHYLLUM AND ArISAEMA DrACONTIUM 45 



may have a corm 4 mm. in diameter while in a well-developed 

 seedling of A. tripJiylliiDi with a strong system of roots and a 

 plumule well grown, the corm may be only 175 mm. in diameter. 

 The enlargement of the corm of A. triphylliiDi becomes marked 

 only after the leaf is well established as a photosynthetic organ. 

 In those seedlings of A. Dracontiuni in which the plumule does 

 not become functional the corm, when its growth is completed, 

 averages 4.5 mm. in diameter. When, however, the seedling has 

 a functionating leaf the corm may attain a diameter of 6 mm. 

 The corm of ^. triphyllum may have a diameter of 5.75 mm. at 

 the end of the season, but in many cases it is much less. 



The enlargement of the hypocotyl is due to the increase both in 

 size and number of its cells. As its growth is rather radial than 

 longitudinal, the epithelial cells become isodiametric in shape. 

 The storage cells increase in size and in number in all directions 

 and so maintain the same relative dimensions. The starch grains 

 contained in these cells are several times as large as those of the 

 endosperm of the seed. The procambium cells of the hypocotyl 

 are very active, dividing both in their longitudinal and transverse di- 

 ameters and the fibro-vascular system soon becomes differentiated. 

 Raphide cells are numerous in the corm and in all parts of the 

 seedlings of the two species. As the corm enlarges, a layer of 

 periderm arises on the outside, from which are cut off tangentially 

 five or six rows of empty flattened cells. In addition to the pro- 

 tection they afford the corm, these periderm cells are instrumental 

 in effecting a separation between the cotyledon and the corm, after 

 the food supply of the endosperm has been absorbed. They 

 grow between the cotyledon and the corm and separate the two 

 by proliferating cells from their surface. In several instances 

 chlorophyl has been formed in the two or three rows directly be- 

 neath the layers of periderm. The only difference in the develop- 

 ment of the corm of the two species lies in the earlier enlargement 

 of the hypocotyl of A. Dracontium and the greater average size of 

 its completed corms. 



The time at which the roots of A. Dracontium appear varies 

 markedly. In some cases the hypocotyl enlarges greatly, becom- 

 ing, as was described above, about 3 mm. in diameter before the 

 first root arises. In other instances the roots are developed as 



