MEMOIRS OF THE NEW YORK BOTANICAL GARDEN. 253 



count for all of the anomalous structures of plants grown in dark- 

 ness. The general relation of this condition to light and darkness 

 will be taken up in the latter part of this paper. 



Etiolation of Leaves. — The observations of the behavior of the 

 stem in darkness showed a uniform reduction of the branches of the 

 main axis of the shoot, but this decreased volume, and extent of the 

 ramifications of the stem was not seen to extend to the foliar mem- 

 bers of the shoot. It will be found most convenient to take up these 

 organs in groups according to their morphological character and the 

 general habit of the plants concerned. An observance of these dis- 

 tinctions leads to the separation of the foliar organs of pteridophytes 

 into two groups, viz., sterile and spore-bearing leaves. 



The etiolated leaves of Lycof odium liicidtiltmi attained less than 

 a half of the normal size and were slightly tinged with green, due 

 to the presence of chlorophyl, which was present in but minute 

 quantities. An erect position was assumed (p. 199). Asplem'um 

 ■platynciwon (p. 75) developed excessively elongated leaves in dark- 

 ness by an increase throughout the entire rachis, and the pinnae 

 were in consequence much more widely separated than in the nor- 

 mal. The pinnae were expanded, but had a superficial area much 

 less than the normal and were more irregularly cut and incised than, 

 the normal, the basal auricled lobe being present in modified form. 

 The mesophyll was but slightly differentiated and the other tissues 

 of the leaf were also in an incomplete condition. Stomata were 

 present, and apparently functional, although not so large as in the 

 normal. The entire leaf was greenish from the presence of chloro- 

 phyl. Etiolated leaves were apogeotropic, but fell over as soon as 

 a length of a few centimeters was reached with the result that the 

 tips soon curved upward. Fully etiolated and extended leaves were 

 capable of some further growth and development when illuminated. 

 No trace of sporogenous tissue could be found on the pinnae. The- 

 stipes of Botrychmm (p. 80) underwent excessive elongation in 

 darkness, the unusual growth occurring in the upper portion, and 

 also in the basal portions of the stalks of the pinnae. The etio- 

 lated stipes were of greater diameter than the normal, and enough 

 chlorophyl was present to give the entire aerial portion a decided 

 greenish tinge. Stomata were present and functional. The epidermal 

 cells were excessively elongated in a degree correspondent to the 

 increased length of the stipe. The laminar rudiments remained in. 



