190 MEMOIRS OF THE NEW YORK BOTANICAL GARDEN. 



than in the stems of old trees in the open, but bore a general re- 

 semblance in occurrence and form to those on juvenile sprouts. 



The walls of the epidermal and underlying tissues of etiolated 

 twigs were slightly tinged with brown and the reddish cell contents 

 of the normal epidermis were entirely lacking. The outline of the 

 cross section of the normal twig is distinctly angular while in the 

 juvenile and etiolated stems it was nearly circular. The subepi- 

 dermal corky layers were present in the juvenile, adult and etiolated 

 branches, the underlying cortex being thickened collenchymatously, 

 pitted, and containing chlorophyl in the two normal forms, while in 

 the etiolated the cortical cells were but slightly thickened, being 

 flattened radially, with some intercellular spaces. The etiolated 

 twigs showed, but a faint development of bast fibers, which with the 

 lack of development of the collenchyma, must account for the 

 mechanical weakness of such stems. The cambium layer is well 

 marked in three kinds of branches, the wood cells and vessels show- 

 ing larger lumina and thinner walls than the normal, although not so 

 large as in the juvenile forms. The same may be said of the pith. 



The epidermal cells of the normal twigs of juvenile, and adult 

 sprouts and twigs show a length parallel to the long axis of the 

 branch fairly equal to the width, being somewhat irregular in out- 

 line, while in etiolated examples these elements are drawn out into 

 more nearly regular rectangles as seen in surface view, being about 

 six times as long axially as tangentially. The tangential width of 

 the epidermal cells was about the same as in normal adult branches. 



The dorsal surfaces of the leaves showed stomata which were open 

 when examined in water, and appear to be functionally active. The 

 duration of the leaf did not exceed twenty days. 



Trees beginning activity in the dark room in May, still bore 

 etiolated shoots in various stages in the following September. 



Jost cultivated some species of maple in the dark room in the 

 winter of 1891 and 1892, and ;found that some of the buds of young 

 trees developed into elongated etiolated shoots. The excess of 

 growth in length was not so marked as in Aescultis, however. It 

 was noted that some secondary thickening, or the formation of an 

 additional ring of wood, was seen near the base of the etiolated shoot 

 in the old stem.^^® 



^"^Jost, L. Ueber Beziehungen zwischen der Blattentwickelung undder Gefassbil- 

 dung in der Pflanze. Botan. Zeitung, 51 : 108. 1893. 



