xi] WATER LEAVES AND POOR NUTRITION [57 



while those grown in a complete culture solution developed 

 their laminae normally. 



The same observer recorded a case in which a plant of 

 Hydrocleis nymphoides^ Buchenau (Butomaceae), which had 

 been bearing the mature form of leaf, was observed to revert 

 to the ribbon form. On examination it was found that most 

 of the roots had died off. When a fresh crop of roots was pro- 

 duced, the mature type of leaf occurred again. 



Another writer^ demonstrated by a series of experiments upon 

 Limnobium Boscii (Hydrocharitaceae) that, in this case also, the 

 heterophylly is not a direct adaptation to land or water life, 

 but that the floating leaves are " Hemmungsbildungen" due 

 to poor nutrition. In Stratiotes aloides^ also, he showed that the 

 stomateless leaves were primary, and that their production 

 could be induced at later stages by unfavourable conditions^. 



An experiment tried by GoebeF on Sagittaria sagittijolia 

 indicated that absence of light in this case inhibits the formation 

 of leaves of the aerial type. An observation of Gluck's on Alisma 

 graminijolium^ Ehrh.*, also points to the same conclusion. But 

 it seems probable that the effect produced in these cases was not 

 due directly to the darkness, but to the state of inadequate 

 nutrition brought about by the lack of light for carbon assimi- 

 lation. 



Among the Potamogetons^, again, experimental work has 

 shown that reversion to juvenile leaves can be obtained under 

 conditions of poor nutrition. For example, when a land plant of 

 P. fluitans^ which had been transferred to deep distilled water, 

 had its adventitious roots repeatedly amputated, regression was 

 obtained to the floating type of leaf and then the submerged 

 type (Fig. 104, p. 158). A similar reversion to thin, narrow 

 leaves was brought about, in the case of P. nutans^ by growing 

 the upper internodes of a shoot as a cutting (Fig. 105, p. 159). 



Waterlily leaves respond to experimental treatment in just 



^ Montesantos, N. (1913). 2 ggg pp ^i_^2. 



3 Goebel, K. (i 891-1893). * See p. 280. 



^ Esenbeck, E. (19 14). 



