122 PLANT HABITS AND HABITATS IN THE 



walls of the innermost central parenchyma are thin. The material 

 examined appeared to be mature, and if so, the lack of sclerenchyma in 

 quantity is a noteworthy feature of the structure of the species. 



ACACIA TARCULIENSIS. 



Acacia tarculiensis is a shrub of compact habit of growth. The 

 phyllodia are broad and numerous, so that the transpiring surface is 

 very considerable. This is in marked contrast to A. aneura and A. 

 linophylla, as will be perceived. 



The phyllodia of A. iarculiensis are of a steel-blue color and the 

 margins have a distinct line of dark brown. In transverse section the 

 following are the most striking structuial features: Chlorenchyma 

 and sclerenchyma alternate beneath the epidermis, the formei lying 

 mainly but not wholly in the shallow hollows of the wavy margin of 

 the section. The bands of supporting tissue are narrow and the 

 cell-walls are not so well developed as in the two species above referred 

 to. The outer epidermal wall is fairly heavy. The guard cells of the 

 stomata are deeply placed and thus are at the bottom of short tubes 

 composed largely of the thickened outer walls. The chlorenchyma is 

 composed of two rows of lather narrow cells which abut on chloro- 

 phyll-free parenchyma, which in turn is situated next to the conductive 

 elements. The latter lie at about the same distance beneath the surface 

 of the phyllode and thus inclose the greatest single portion of the 

 tissues, namely, the chlorophyll-free interior parenchyma, which is 

 made up of relatively large cells. 



Trichomes of whatever sort do not appear to be a feature of the 

 phyllodia "blades" or lamina. On the "blades" of the older phyllodia 

 only very widely scatteiing remains of trichomes are to be found. 

 These appear to be of two kinds only, namely, a short-stalked and 

 small secreting hair and a larger and two-armed covering hair. The 

 material did not show the hairs to advantage, but suggested that they 

 are not plentiful. The most striking trichomes of the phyllodia, 

 however, are to be found only along the margins and are composed 

 of chains of cells, the terminal one being the largest, all of which, 

 in the herbarium material studied, are dark brown in color and appear 

 to be secretory. The outer edge of the blade of the phyllode is covered 

 heavily with a nearly colorless material, the nature of which I did not 

 attempt to learn, but it gave evidence of having originated in the hairs. 

 It is probable, therefore, that the trichomes are glandular. The origin 

 of the hairs was not determined. The tissues immediately beneath 

 these hairs, to a depth of 3 to 4 cells, is discolored in a fashion analogous 

 to that of the hairs themselves. The cells are otherwise colorless, 

 small, and have a curious appearance of being in the process of division 

 on a plane parallel to the leaf margin. A noteworthy strand of con- 

 ductive tissue underlies the marginal tissue just referred to. 



