78 



MEMOIRS OF THE NEW YORK BOTANICAL GARDEN. 



formed by March 6, 1901. The midrib was about a millimeter in 

 diameter midway between the tip and base. The pinnae were rep- 

 resented by flattened expansions 1.5 by i mm. with oblique auricled 

 basal lobes. Later three or four pairs of lobes could be made out 

 in the pinnae. The lower (outer) surfaces of the pinnae showed 

 numbers of stomata with a circular outline, which were slightly open 

 when examined in water. The guard cells, as well as the spongy 

 parenchyma, were richly loaded with chloroplasts containing chloro- 

 phyl, and the entire plant above the soil has a decided green color. 

 An examination of the structure of the pinnae revealed the fact 

 that the fibrovascular tissues were in a very primitive stage of devel- 

 opment. The mesophyll were but slightly differentiated, and inter- 

 cellular spaces were very sparse. 



An etiolated culture was brought into the 

 light on April 2, and the older pinnae under- 

 went but little structural change except in the 

 formation of additional chlorophyl. Pinnae 

 of the younger fronds, which had accom- 

 plished but little growth at the time of illumi- 

 nation attained a stature more nearly that of 

 the normal, and the differentiation of the tis- 

 sues was carried out in much the usual man- 

 ner. It is to be noted also that such pinnae 

 stand much farther apart than the normal, 

 showing an excessive elongation of the midrib. 



Aster divaricatus L. 



Rootstocks of Aster divaricatus were 



brought into the dark room in February, 1900, 



and soon showed a rapid growth of the shoot. 



Fig. 33. Aster divarica- Etiolated stems attained a height of about 35 



tHs. ^, normal leaf. ^, eti- ^^^ which is not far from the average of the 



olated leaf. , ^ ^. , _ ^ . , 



normal plant, rifteen leaves were formed 



on a , typical specimen, with petioles about 5 to 6 cm. long. The 

 laminae were about 2 cm. long and i cm. wide when unrolled. The 

 upper surfaces (inner surfaces) remained appressed together, only 

 partially separating in a few instances. The petioles held a position 

 from 30 to 40*^ from the vertical, or rather from the stem. The 

 hairs on the normal stems were equally abundant on etiolated organs. 



