MEMOIRS OF THE NEW YORK BOTANICAL GARDEN. 



79 



Normal stems have 

 several collenchymatous 

 subepidermal layers. 



But one or two layers of 

 subepidermal tissue were 

 thickened in the etiolated 

 culture, and only to a 

 slight extent. The inter- 

 cellular spaces were quite 

 as well marked in etiolat- 

 ed cultures as in normal. 

 The bast fibers were only 

 slightly thickened and 

 no cambium layer was 

 formed in etiolated cul- 

 tures. Full differentia- 

 tion of the sieve cells was 

 not accomplished. The 

 bundles are separated by 



Fig. 35. As/er divaricatus. 

 verse section of etiolated stem, 

 in Fig. 34. 



Fig. 34. Aster divaricatus. i, partial transverse 

 section of normal stem. 2, partial cross- section of 

 etiolated stem. A, epidermis. B, collenchymatous 

 tissue. C, cortex. Z>, bast fibers. £, cambium. 

 F', xylem. G, pith. 



wide primary medullary rays, 

 and the formation of secondary 

 tissues had not begun in etio- 

 lated stems. The xylem shows 

 a development arrested before 

 the vessels had reached nor- 

 mal condition, and the pith 

 lacked some of the intercellular 

 spaces found in the normal. 

 Etiolated shoots did not sur- 

 vive very long and the earlier 

 leaves quickly disappeared 

 before the older ones were 

 formed. 



Results similar to the above 

 were obtained from an un- 

 known species which was cul- 

 tivated later. 



Partial trans- 

 Description as 



