352 YOUNGKEN— ON THE MYRICACEAE 



those of M. cerifera are 33.99 m x 26.22 n and of M. Carolinensis, 63.34 n x 

 33.46 At; the mesophyll region is narrower than that of M. cerifera, 

 broader than that of M. Carolinensis; the lower epidermis has cells 

 whose outer walls in surface view show a mean measurement of 37.87 /x x 

 21.85 }x, while those of M. cerifera are 36.42 x 24.28 and M. Carolinensis 

 54.87 MX 23.30m; fewer unicellular simple trichomes on upper epidermis 

 than those of M. Carolinensis, more than those of M. cerifera. 



They resemble those of M. cerifera in that both red and golden- 

 yellow headed glandular hairs are present on the lower surface and also 

 by the fact that their upper epidermis has a cuticle of about equal thick- 

 ness. 



They resemble M. Carolinensis in that they have few crypts on the 

 upper epidermis containing golden yellow glandular hairs. The mid 

 rib and stronger veins are completely surrounded by a zone of scleren- 

 chyme and connected with the upper epidermis by collenchymatic cells. 



Comparative Morphology of the Roots 



The roots of M. cerifera, M. Carolinensis, M. Macfarlanei, M. Gale 

 and Comptonia asplenifolia show the general structure of Dicotyledons. 

 All of the younger ones which the writer has examined possessed a root 

 cap, above which were noted numerous root hairs with the exception 

 of those of M. Gale which possessed relatively few. 



The subapical region showed three groups of generative tissues which 

 form the calyptra and epidermis, cortex, and central cylinder. 



The radicle grows downward in a rather tortuous manner and forms 

 the fibrous tap root, which in the above named species is soon exceeded 

 by the lateral roots borne on the hypocotyl axis. 



Primary Structure 

 The piliferous axis is composed of large clear pavement like cells, 

 which frequently elongate into root hairs. The cortex is composed 

 of 5-12 layers of cells, the most external layer of which is deprived of 

 intercellular air spaces and collenchymatic. The other layers are com- 

 posed of rounded to polygonal cells arranged in somewhat loose radial 

 rows extending to the endodermis. The air spaces in M. Gale and M. 

 Carolinensis growing in humid earth are very large. Some of the cells 

 of this region contain rosettes of calcium oxalate, others tannin, occa- 

 sionally gummy Hgnin. 



