246 MEMOIRS OF THE NEW YORK BOTANICAL GARDEN. 



weeks, the growth in the dark always ceases, and the whole plant 

 become diseased and perishes ; in many cases, as with P/iascoIuSy 

 etc., not until all the reserve-materials of the seed have been com- 

 pletely used up for the formation of organs ; in other cases, however, 

 as with the gourd, growth and the development of organs cease while 

 the cotyledons still retain considerable quantities of unused formative 

 substance." My own experiments lead to the conclusion that etio- 

 lated growth is indeed not possible beyond the capacity of the stored 

 formative substance, but the ability of the plant to use all of this 

 material depends upon other factors, which are in fact the principal 

 causes to which the characteristic form of etiolated plants is due. 

 Without further discussion of these causes at this time it may be re- 

 garded as quite well founded that the death of etiolated seedlings, or 

 adult plants in darkness, is generally due to the incapacity of the im- 

 perfectly differentiated conducting tissues, or to the destruction of the 

 reserve-material by disintegrating or fermentative processes. The 

 development of the transpiratory system must also be taken into ac- 

 count in the consideration of the mechanisms for translocation of 

 material in the plant. 



Influence of Etiolation on the Development and Differentiation 

 of the Tissues and Emergences. — The meager facts recorded, con- 

 cerning the effects of darkness and light upon trichomes, in my own 

 observations are not sufficient to furnish a basis for any generaliza- 

 tions upon this subject, and previous investigations have been made 

 under various conditions of imperfect and partial etiolation. Hairs 

 are ordinaril}'^ present on the aerial stems of Apios, but were lacking 

 from etiolated stems, although present in subterranean shoots, which 

 the stems grown in darkness resembled in some particulars (see 

 page 42). Etiolated hairs of Hydrastis were only about one-fourth of 

 the size of the normal both on the stem and leaves, although the former 

 was unduly elongated and the latter reduced. The stalked glands 

 of Lysimachia were unchanged on stems which underwent excessive 

 elongation, and did not appear so numerous in Mcnis^ermuni, although 

 of about normal size. The hairs of Popiilus were smaller than the 

 normal, although the other epidermal elements were much elon- 

 gated. No marked alterations could be seen in the hairs of As/er, 

 Cornus or Pagus, although the first two species exhibited excessive 

 elongations of the stems on which these structures were borne. The 

 prickles of Sniilax were both more slender and shorter on etiolated 



