ELLIOTT: VARIATIONS OF QUERCUS. 



49 



cells in sq. mm. : No. 1, .000542 ; No. 2, .000503 ; No. 3, .000604 ; 

 No. 4, .000661. (Figs. 45 to 48, sec. A.) 



MESOPHYLL. 



In the bleached leaf the palisade cells of No. 2 were seen to 

 be much more numerous and densely crowded together than in 

 the other three oaks. The palisade cells of No. 1 were smaller 

 than the others, but aside from these differences the mesophyll 

 was of no value in classification. The spongy parenchyma was 

 not discernable in the bleached leaf, but tangential sections 

 from paraffin-imbedded material showed that the cells of No. 1 

 and No. 4 were generally smaller than those of Nos. 2 and 3. 

 These cells, however, varied greatly in the same leaf. 



In cross section the palisade cells of No. 2 were seen to vary 

 greatly in length, while those of the other oaks were more uni- 

 form. (Figs. 27 to 30.) 



VENATION. 



Aside from the macroscopic differences already noted, the 

 only constant differences in venation was in the distance apart 

 of the vein endings. These varied in order: No. 2, 1, 3, 4, 

 with No. 4 having the closest venation and No. 2 the most open 

 venation. (Figs. 49 to 52.) 



This summary might serve as a key to classification, and 

 with this idea in view all the oaks with leaves similar to the 

 four types here studied found in the herbarium were examined 



