TRIPHYLLUM AND ArISAEMA DrACONTIUM 41 



Strands which foreshadow the bundles have already been laid down 

 in the cotyledon, stem-bud and hypocotyl. Near the tip of the 

 cotyledon the procambium strands branch and anastomose irregu- 

 larly and therefore no definite number or arrangement of them 

 can be determined, but at the base the number becomes constant 

 and each strand occupies a regular position. The plan of arrange- 

 ment in both species is similar. In cross section the strands mark 

 out' a crescent in which the largest is at the middle of the bow. In 

 A. tyiphylltan which has regularly five strands, two lie on either 

 side of the central ones, while the cotyledon of A. Dracontium 

 shows the same arrangement of its five principal strands, but has 

 in addition one or two smaller ones. When there are two, these 

 extra strands occupy positions on either side of the large middle 

 trace. When only one extra strand is retained, it invariably is at 

 the right. In the tubular portion of the cotyledon, the largest 

 strand is in the thickest part of the wall. The strands are com- 

 posed of six or seven rows of narrow elongated cells which have 

 their long axis four to six times the length of their radial, and 

 parallel with the longitudinal axis of the embryo. In the stem-bud, 

 procambium strands have also been differentiated. In A. Dracon- 

 tium the strands in the plumule are faint and there is some varia- 

 tion in the number of the procambial regions. They are never 

 more numerous than three and at times only the pro-cambium 

 of the future midrib has been laid down. In A. triphylliim five 

 distinct procambium regions can be distinguished in the plumule. 

 Procambium strands are also present in the hypocotyl and occupy 

 fully one half of its entire diameter. They are continuous with 

 the procambium of the stem-bud and form at the base of the 

 hypocotyl the rudimentary root stele. At the base of the hypo- 

 cotyl the root-cap may be distinguished, made up of several rows 

 of rather large cells which stretch across its entire base and are 

 continuous at the sides with the dermatogen of the embryo. In 

 the outer rows the cells are empty. Meristem tissue is to be found 

 at the stem-bud and at the base of the hypocotyl where the root 

 takes its origin. These cells are very small and nearly isodia- 

 metric. Their nuclei are large and fill almost the entire cell. 

 Parenchyma cells make up the rest of the embryo. They are two or 

 three times the size of the epidermal cells and are packed with 



