[LLOYD] ORIGINATION OF ASCIDIA 79 



conjoined margins of neighboring lobes, does not result from the 

 secondary fusion of primarily free margins, but rather from the upward 

 growth of the meristematic tissue included between closely adjoining 

 edges or between (lower) surfaces. The bridging over of a wide 

 sinus between lobes, (as found in the leaf represented in figures 11 

 12, & 12 a-d) by tissues pertaining to the morphological lower side of 

 the leaf is also not due to fusion, but to the upward and transverse, 

 more rapid growth of these tissues as compared with the adjacent 

 tissues pertaining to the upper side. That the fusion of primarily 

 free parts may occur during the development of ascidia is suggested 

 by one case (Trifolium) described by Gager (I.e.) in which the "margins 

 of the leaf adhere only at their distal portions." But this case was 

 not examined to see if the separation toward the base was not itself 

 secondary, in which even the "fusion" w^ould be primary (congenital 

 conscrescence). In the cotton plant, there occur indications that 

 secondary disruption may be expected occasionally. I refer to the 

 slight amount of local histolysis along the lines of concrescence as 

 shown in figure 7a. One may here recall a similar condition found in 

 the flowering internode of the same plant, in which two organs of 

 dissimilar growth capacities are congenitally concrescent and between 

 which a disruption of tissues is rather common. '^ 



For the reason however, that destruction of tissues is not a constant 

 concomitant of the abnormalities herein described, if indeed it ever 

 occurs, it seems impossible to identify them with tomosis^ so called 

 by O. F. Cook. This disorder, consisting in local destruction of 

 cells, but unaccompanied by other abnormality, appears in cotton 

 seedlings in the field when they are subjected to alternating extreme 

 conditions possibly including frost. It appears to be secondary, 

 being caused after the exposure of the young leaf is accomplished. 

 Cook,^ however, in the same connection describes "scars" which he 

 refers to the earlier imposition of the same causes. He says: "And 

 in addition to the open wounds that result from leaf-cut there are 

 usually some that have healed, giving a characteristic torn-and-mended 

 appearance. Such scars, like other leaf-cut wounds, often lie in a 

 somewhat radiating position between the principal veins. Healing 

 of wounds and regeneration of lost parts show that the injuries are 

 liable to occur at a very early stage in the development of the leaf. 



•Lloyd, F. E. Abscission. Ottawa Naturalist. 38: 41-52; 61-75. Aug. and 

 Sept. 1914. 



-Leaf-cut or tomosis, a Disorder of Cotton Seedlings. Circ. 120 Bur. PI. Ind. 

 U.S. Dept. Agri., April 5th, 1913. 



3Cook, I.e. p. 30-31. 



