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TliL' DelGrmhintiv*; Action of Environ in Factors Upan Neol)eckiaac<inatica Greene. 277 



The full series of foliar organs of Neobeckia ranges from broadly 

 oblong lanceolate or ovate leaves in the nepionic stages to narrowly 

 ovate or lanceolate floral bracts in the senescent stage. The mature 

 or adult leaf of the highest type in aquatics is cut into fine thread- 

 like divisions, and the mature leaf of terrestrially grown plants is much 

 divided with narrow strap-shaped segments (Fig. 4 and 5). The spread 

 and size of the nepionic leaves varies with the conditions under which 

 they are formed. The structure of the mature leaves varies between 

 the limits of the two types indicated according to the environment 



Nepionic leaves show a more pronounced development of the 

 lamina on free cuttings than on awakened lateral buds on entire stems, 

 on the upper parts of thickened root-stocks rather than on the lower. 

 Cuttings placed in water invariably produce nepionic forms immediately, 

 but when the water is allowed to evaporate leaving the plantlets growing 

 as terrestrials the type of leaf changes gradually from the aquatic to the 

 terrestrial type without the intervention of nepionic forms. Abrupt change 

 from aquatic to terrestrial conditions however is followed by the inter- 

 position of nepionic types indicative of rejuvenescence. Anchorage of 

 floating aquatic plantlets while submerged was followed by modification 

 of the aquatic leaves toward the terrestrial types without the inter- 

 position of nepionic forms. Anchorage and exposure of the stems to the 

 air would occur together under natural conditions, but either may bring 

 about the modifications ensuing when the two act together. 



The development of nepionic leaves indicative of rejuvenation 

 occurred in terrestrial cultures with the change from cool to warm 

 seasons, from warm to cool conditions, with rapid changes in the supply 

 of moisture either way, and might also be induced simply by the 

 increased aeration following stirring of the soil about the roots, 



Aquatically grown plants remained alive when placed in strong 

 (10 Vo) solutions of potassium nitrate, but the aquatic leaves were killed. 

 Terrestrially grown plants retained the strap-like divisions of the leaves 

 unharmed under the same conditions; the terminal buds remained inactive 

 but the lateral buds were awakened unfolding the broadly laminar 

 nepionic leaves of the customary type. In this connection it is pertinent 

 to call attention to the fact that the aquatic leaves, and the main 

 actively growing points would be most easily dehydrated and to an 



f injurious extent by the solution. The terrestrial leaves and the lateral 



buds would endure the concentration and in case of the latter undergo 



I the changes Avhicl* constitute the basis of rejuvenation. 



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