MEMOIRS OF THE NEW YORK BOTANICAL GARDEN. 217 



excessive elongation of the petioles when confined in darkness, and 

 Saurtirus ceriums (see page 179) developed stems in excess of the 

 normal length under the same conditions. It is to be noted that these 

 three species are, properly speaking, bog plants and support their 

 inflorescences and foliar organs above the level of the water. A 

 similar behavior has been reported for Hiffui'is vulgaris^ Ranunculus 

 dtvaricattis and Myj'ioj^hyllum sficatum by Mobius, so that the 

 evidence is fairly conclusive that aquatics or semi-aquatics, which 

 carry up the shoots irrespective of the exact height of the water level 

 agree with land forms in their etiolative reactions.'" 



The results attained by Mobius with other forms are fairly in 

 accord with those of Frank so far as the action of stems is concerned. 

 JSfaias major', Cabomba, Chara and Callitriche showed no special 

 reactions to confinement in darkness. PhiJotria Canadensis {Elodea 

 Canadensis^ and Cerato^hyllum demersuni occupy a position mid- 

 way between the two groups of forms noted above. Both species 

 are rooted aquatics with the shoots wholly submerged, and yet show 

 an exaggerated elongation of the internodes in darkness, even when 

 torn from their anchorage and allowed to float freely in the water. 

 The flowers of Ceratophyllimi are borne in submerged axils, and 

 those of Philotria float on the surface, the staminate ones becoming 

 detached and rising to the surface when mature. These etiolative 

 elongations are accompanied by various reflexive movements of the 

 leaves in Ceratophyllum and Myriophyllimi. No explanation is at 

 hand to account for the characteristic behavior of the two forms noted 

 above. It may only be said that these two plants are exceptions to 

 the rule that submerged and floating aquatics are not capable of 

 etiolation. It is to be noted in this connection that the submerged 

 forms of at least some of the species with dimorphic leaves are due 

 to the osmotic action of the salts dissolved in the water, or rather to 

 the amount of water held in the vacuoles of the primordia. This 

 has been shown to be the case in Proserpinaca palustris and is very 

 probably true of other forms also.'^^ 



The elongated cylindrical prolifications formed by Caulcrpa in 

 darkness may be taken to be due in part to the specific influence of 



^5' Mobius, M. Ueber einige an Wasserpflanzen beobachtete Reizarscheinungen. 

 Biol. Centralblatl, 15: i, 33. 1895. 



1*^ MacCallum, W. B. On the nature of the stimulus causing the change of 

 form and structure oi Proserpittaca palustris. Bot. Gazette, 24: 93. 1902. 



