TRIPHYLLUM AND ArISAE.MA DrACOXTIUM 47 



structure and the secondary roots are tetrach as a rule. Some, 

 however, have been observed to be triarch ; in A. tripliylhim both 

 primary and contractile roots are triarch. After the contraction 

 of the roots the outer cortex cells are very much strained and 

 twisted, but the radial elongation of the inner cells protects the 

 stele from any distortion. The roots of A. Draconthini are more 

 variable in all respects than those of A. tripliyllum. 



The stem-bud of A. Dracontiiim and A. triphyllinn have the 

 same structure in the resting embryo, with the exception that the 

 procambium stands in the bud leaves have reached a more 

 advanced stage of differentiation in A. triphyllinn. During 

 the first season's growth, however, the structure of the bud in 

 the two species has an entirely different history. Like the 

 roots the plumules of the A. Dracontium seedlings vary greatly 

 in the state of development which they attain. As a rule the 

 plumule of A. Dracontinui develops to at least a small degree 

 after germination, forming a lamina and a short petiole which al- 

 though it may break through the cotyledonary sheath, yet rarely 

 reaches the air and is often represented only by a rudiment 2 mm. 

 in length remaining permanently enclosed by the cotyledon and en- 

 wrapping in its turn the stem-bud of the next year. This undeve- 

 loped plumule is cut off at the end of the season by the formation 

 of a periderm between it and the corm in the same way as the coty- 

 lendon is separated from the corm. About 10 per cent, of the 

 seedlings of A. Draconthini produce functional plumules. They 

 appear at different stages during the growth of the corm, gener- 

 ally when it has already attained a considerable size and in some 

 cases only after the seedling has entirely separated from the seed. 

 Its method of emergence from its enclosing cotyledon is exactly 

 the same as that of A. triphylluui which produces a plumule nor- 

 mally. As soon as the root has secured a firm hold on the soil 

 and the hypocotyl is only slightly enlarged, the plumule with its 

 blade recurved parallel to the petiole and rolled in at the mar- 

 gin breaks through the tubular part of the enclosing cotyledon 

 through a longitudinal slit which is already present in the resting 

 embryo. The plumule becomes green rapidly while the petiole 

 at the base of the lamina straightens out and the folded blade un- 

 rolls and grows larger. 



