286 MEMOIRS OF THE NEW YORK BOTANICAL GARDEN. 



but a glance at such etiolated shoots and leaves as those of Aster, 

 Bozviea, Pastinaca, Peltandra, Phytolacca, Populiis, Sai'racenia, 

 as well as those of the floating aquatics to demonstrate that the abnor- 

 mal forms asstimed by these plants could not be interpretated, even 

 by the most generous allowance, as being adapted to reaching out to 

 light, or even of maintaining an economical existence during its ab- 

 sence. On the contrary many species exhibit phenomena the reverse 

 of useful, such for instance as the increased diameter of the stems 

 and the positions of the various organs. That some species are cap- 

 able of adaptations by which shoots or leaves deprived of light make 

 excessive and rapid elongations which have the effect of carrying the 

 apical portion up more rapidly and to greater distances than the 

 normal is to be admitted. Such capacity is to be seen in such forms 

 as Arisacma in which the perennial portion of the plant lies deeply 

 buried, and the growth of the aerial members continues until the ex- 

 posure to light acts as a stimulus which checks further effort in this 

 line. It is to be clearly understood however, that such action is not 

 purely etiolative in its character, but is in fact an adaptation of 

 which the plant is capable when etiolated, and that not all plants 

 have acquired this habit or power of adaptation to darkness, although 

 all green plants undergo etiolative alterations in addition to those 

 accompanying the non-formation of chlorophyl. Etiolation is there- 

 fore not an adaptation to darkness, and the forms assumed by plants 

 in darkness are not necessarily, or primarily, due to an effort on the 

 part of the plant to attain exposure to light. The various phenomena 

 of etiolation are due to the absence of light in the first instance, and 

 the forms assumed by plants in this condition may, in some cases, be 

 modified in such manner as to be of benefit to the plant by enabling 

 it to make an effort to thrust its leaves or shoots up into light. This 

 statement applies to the fungi also, some of which have been found 

 to show etiolative adaptations of this character. 



Relation of Light and Darkness to Growth, and to Differentiation 

 and Development. — Doubtless the most important and basic fact 

 common to all species, not including degenerate chlorophylless 

 forms, is that the tissues of etiolated organs do not show the same 

 degree of morphological differentiation as may be found in corre- 

 sponding members of the same age exposed to illumination. The 

 tissues of stems,, leaves and floral organs undergo only limited de- 

 partures from the embryonic, or bud-condition, when grown in dark- 



