1B20 Pease; on Desmarestia 333 



ing visible to the naked eye only by the filmy appearance which they 

 give to the edges of the ultimate pinnules. They are set much more 

 closely together and hence do not appear to be in tufts, as Oltmanns 

 (1904) illustrates them for D. aculeata (Plate 59, Fig. 1). Manj' of the 

 hairs, especially those arising near the base of the j^innule, are short and 

 simple, and of less diameter than the more vigorous branched hairs to- 

 ward and at the distal end. The main axis of the hair, formed by cells 

 cut off form the upper side of the intercalary growing point, may con- 

 sist of from 10 to 50 cells. The hair is spindle-shaped. The youngest 

 cells, next the growing point, are about 100 micra wide and 15 or 20 

 micra long. The largest cells, about its middle, are 125 to 200 micra 

 in diameter and 175 to 225 micra long. The tip ends in a small conical 

 cell about 37 micra wide at the base and 45 to 70 micra long. The individ- 

 ual cells are slightly distended in the middle, and thus barrel-shaped. 



In branched hairs, the branches arise as outgrowths on the sides of 

 the cells of the main axis, which are soon cut off by cross walls. A cell 

 thus cut off divides again and the branch elongates by repeated division, 

 this always occurring in the innermost cell, so that the hair branch develops 

 basipetally. These branches, like the axis from which they grow, are 

 spindle-shaped, with a conical end cell. Although the lateral branches 

 of the central axis below the growing point always arise in pairs, and both 

 members of the pair persist, so that branching is always opposite, the 

 lateral branches above the growing point quite often arise singly, and sever- 

 al single branch hairs in succession may be produced, either on the same 

 or on opposite sides of the axis (Plate 62, Fig. 1). In fully grown hairs, 

 both proximal and distal ends of the axis, which are respectively the young- 

 est and oldest regions, are devoid of branches, while in the intermediate 

 region branches are closely crowded. In this crowded region every cell, or 

 every second or third cell, bears a pair of branches, or occasionally only a 

 single branch. Usually, from 3 to 10 cells of the axis bear branches, and 

 the first 10 to 15 cells at the distal end of the axis are devoid of branches. 

 The branches themselves consist of from 5 to 15 cells each and do not 

 branch again, as they sometimes do in D. aculeata. 



The writer has examined the assimilating hairs in D. aculeata and 

 D. viridis as well as in D. Ugulata, and finds that the size and shape of 

 the cells and also the arrangement of the branches is different in each 

 species. It would be interesting to examine the assimilating hairs of other 

 species. It may be possible that this could be made one of the distinguish- 

 ing characters in separating species. 



At the end of the growing season all the assimilating hairs are shed, a 

 definite method of abscission being quite apparent. Entire pinnules were 

 stained in Bismarck brown, cleared in cedar oil, and mounted in balsam. 

 The tissues are so transparent that one can focus through the cortical layers 



