LOVEJOY: ANATOMY OF G^RTNERIA. 279 



in its inner part, with a cutinized outer layer .001 mm. in 

 thickness. 



There are approximately 371 stomata per sq. mm. on either 

 side of the leaf, nearly the average number found in plants, 

 and there seem to be no essential differences in size and shape 

 of the stomata on the two sides of the leaf. Projecting above 

 from the side walls of the guard cells adjoining the air pas- 

 sages are the ridge-like protuberances or rims characteristic 

 of guard cells. (Fig. 31.) These pore structures are highly 

 cutinized and approximate when the stoma closes, thus ma- 

 terially reducing transpiration. The guard cells of Giertneria 

 are normally at the level of the general epidermis, rarely ris- 

 ing above it; but in the case of a leaf infected by a fungus, 

 a curious modification of the epidermis tissues occurred, the 

 outer tangential wall becoming highly thickened, and the guard 

 cells being sunk below the surface. (See fig. 34.) 



Two distinct varieties of hairs appear on the leaf, namely, 

 elongate uniserial clothing, and short, two-ranked glandular 

 hairs, these two forms making up the typical hairy covering 

 of the Compositse. (Solereder, 1908.) 



The uniseriate clothing forms are much the more numerous 

 on the leaf, being seen under the microscope as a thick mat on 

 the leaf surface. (See fig. 32.) Their association in the epi- 

 dermis is shown in figures 33 and 27, where they are seen to 

 be outgrowths of single epidermal cells. 



The short two-ranked hairs belong to the class of external 

 secretory organs, widely distributed throughout the Com- 

 positse. They are regularly biseriate, short-stalked or appear- 

 ing as sessile, and have all walls entirely cutinized. They 

 secrete a substance that has a golden-brown color in formalin 

 solution. This substance from formalin material is soluble in 

 ether and alcohol, and when dissolved out by this means there 

 is left in each cell of the gla^id a nuclear body. These are rela- 

 tively large and appear to be intimately associated with the 

 secretion of the brown substance. 



The Fimdameyital Leaf Tissue. 



The fundamental or mesophyll tissue shows the typical leaf 

 structure of palisade and spongy parenchyma, with the occa- 

 sional occurrence of bast fibers and stone cells subtending the 

 veins. 



3-Univ. Sci. Bull.. Vol. VII. No. 16. 



