200 Evans: Notes on genus Herberta 



leaf. A case in point is found in iJ. adunca. According to Ste- 

 phani the branches of the vitta come to an end below the apices of 

 the divisions; according to K. Miiller they extend to the apices. 

 At the same time the value of the vitta from the standpoint of 

 taxonomy must not be overlooked, and Stephani deserves credit 

 for utilizing it. 



The cells of the vitta present a number of interesting peculi- 

 arities, not only in their structure at maturity but also in their 

 development, especially in the way in which the thickenings of the 

 wall are deposited. Gottsche, in his account of H. juniperina* 

 noted some of these peculiarities many years ago, but subsequent 

 allusions to them have been very scanty. According to Gottsche 

 each basal cell of the leaf, after treatment with caustic potash 

 and iodide of zinc, reveals a spiral of eight to fifteen turns repre- 

 senting a thickening of the secondary layer of the wall. In a 

 later accountf of the same species he gives the number of turns as 

 fifteen to twenty- two. 



By treating young leaves with potash it is easy to demonstrate 

 the presence of the bands of thickening described by Gottsche, 

 not only in the basal portion of the leaf but elsewhere, and they 

 clearly represent a stage in the development of the cell wall 

 (Text fig. ii). The writer has found it impossible, however, to 

 show that the bands form a continuous spiral. They seem to be 

 rather in the form of separate rings or partial rings, an occasional 

 ring being branched. When the rings are incomplete the gaps 

 occur on the free walls of the cell and never on the vertical walls, 

 which separate the cell from its neighbors. Even under these 

 circumstances, however, the bands of thickening extend partially 

 across the free walls and leave only the median portion thin 

 throughout. The bands of one cell do not lie opposite the bands 

 of adjoining cells but tend to alternate with them. The vertical 

 walls show a zigzag appearance where they meet the free walls, 

 each angle of the zigzag marking the position of one of the bands. 

 In the irregular cells between the vitta and the margin the bands 

 are more irregular than in the cells of the vitta and rarely if ever 

 form complete rings. In other respects they are essentially the 

 same. 



* Rabenhorst, Hep. Eur. 210, accompanying text, 

 t Mex. Leverm. 138. 1863. 



