STOUT: DUPLICATION AND COHESION ^ 481 



continuation of the other and more branches and leaves are produced 

 upon the two than upon a single stem. Branches and leaves occa- 

 sionally develop, however, from the very center of the grooves and the 

 bases of leaves thus placed often extend across a side of both stem- 

 elements. Such leaves and branches are always simple as far as I 

 have observed. In the uppermost portions of the stem the phyllo- 

 taxy is often completely regular, but immediately above the seg- 

 ment of noticeable duplication the phyllotaxy is irregular and this 

 irregularity may extend to the apex or terminate in the banded type 

 of fasciation. 



Torsion is frequently seen. The two elements may twist about 

 one another in spirals with the two parts equal in development and 

 the spirals in the same direction. In other cases the two stem-ele- 

 ments exhibit incompatible growth either as to direction of torsion 

 or rate of growth, or both, and mechanical lesions result. These tear 

 apart the two elements or often cause one to break, thus producing 

 much irregular and twisted development of the main axis. Various 

 conditions which thus arise are shown in Plate XII . Usually the lateral 

 branches above such lesions are poorly developed (no. 9), the more 

 vigorous growth being seen in the lower laterals. 



In this strain of red-leaved Treviso, irregularities of development 

 are seen in the growth of the cotyledons. For most seedlings two 

 quite normal and separate cotyledons are produced as shown in nos. 

 I, 2, and 4 of Text Fig. i. In numerous cases even of sister plants the 

 two cotyledons are fused ; only the basal portions of the stems may be 

 fused as in nos. 5, 6 and 15, or the fusion may extend upward 

 toward the apex as shown in nos. 7, 8 and 9. In some cases 

 what appears to be only one cotyledon is in evidence, as shown 

 in nos. 10, ii, 12 and 16; either the two have become completely 

 fused or the growing point of one failed to develop. The very 

 complete series of stages of fusion leading to a single cotyledon 

 suggests that the initial growing points of the two cotyledons may 

 completely fuse or perhaps are never differentiated. There are also 

 numerous cases of crumpled and irregularly developed cotyledons 

 either in one or both of a pair or in a single one, as may be seen in 

 nos. 3, 13, 14, 15 and 17. 



In only two cases have I observed any tendency to an increase of 

 cotyledons; in each of these seedlings one of the cotyledons was some- 

 what bisected, as shown in nos. 19 and 20. The duplication seen in 

 the main axis is not accompanied by duplication or increase in the 

 normal number of cotyledons. 



In a very few instances there is no development of the plumule. 

 This may occur in seedlings having two normal unfused cotyledons as 



