1 66 



MEMOIRS OF THE NEW YORK BOTANICAL GARDEN. 



tion of phellogen was found, although it was marked in the corre- 

 sponding region of normal stems. The cortical cells in the etiolated 

 appear to be smaller than in the normal stem, and more compactly 



arranged. The bast fibers 

 form a continuous irregular 

 circle in the cross section of 

 the normal stem but were still 

 separated by the medullary 

 rays in the etiolated. 



The more interesting 

 differences of structure were 

 to be found in the lower and 

 older parts of the stem. The 

 epidermis and hypodermal 

 cells in the etiolated had be- 

 come irregular and were 

 slightly collapsed. A phel- 

 logen had been formed in 

 the medio-cortex, and the 

 cortical cells were somewhat 

 larger than in the normal, 

 and with thinner walls. The 

 difference between the bun- 

 dles of bast fibers was still 

 very marked. The sieve 

 tissues showed a diameter 

 about half that of the nor- 

 mal, and the cambium layer 

 was not so well marked as in the normal. The elements of the xylem 

 were in general larger in all dimensions, but the thickness of the 

 xylem ring was hardly half that of the normal. The walls of all of 

 the tissues in the xylem were thinner. (Figs. 123-126.) 



The petioles showed corresponding differences in the normal and 

 etiolated. The epidermal tissues were less thickened, and no col- 

 lenchyma was to be seen. The separate bundles of the meristele 

 were in a very rudimentary stage, with the sieve tissue but imper- 

 fectly developed, and the pericycle entirely lacking. The bundles 

 were clearly separated by rays of parenchymatous tissue. (Fig. 121.) 

 A seedling of an unknown ^lercus was brought into the dark 



Fig. 127. ^uercus sp. Seedling in second 

 year. Normal (obliqvie) and etiolated branches. 



