272 



Mac Dougal^ 



The growth of the species as a terrestrial entailed among otlier 

 departures from tlie experience of the plant the endurance of a great 

 range of temperature during the year and also daily. It was notable 

 tliat full maturity of the plant was not reached under such circum- 

 stances until conditions were provided in which this feature was of a 

 character approximating that of the habitat of the plant Individuals 

 grown as terrestrials in the glass house of the Desert Laboratory were 

 taken to the Coastal laboratory in October 1910- The climate was oceanic, 

 the temperature falling below the freezing point but a few hours in 

 each yeafj and the total exposure above 70^ F is comparatively small. 

 Under such conditions elongated aerial stems with narrow senescent 

 leaves were formed in 1911 and in 1912, while in 1913 one plant 

 proceeded to the development of full inflorescence. 



Fig. 10. Cross section through a ter- 

 restrial leaf segmenJ of Neobeckia. 



Fig, 11. Cross section through a part 

 of a leaf from the terminal part of a 



stem of Neobeckia. 



A comparison of the structures of aquatic and terrestrial plants 

 was made from material grown in the New York Botanical Garden. 

 The first lot of cuttings were placed in the soil in pots in 1902. These 

 soon underwent rejuvenescence, sending out roots and beginning with 

 the formation of the oblong-ovate nepionic leaves which were followed 

 by the usual series of aerial dissected forms. The epidermal elements 

 of such leaves were flattened but the parenchymatous elements were 

 arranged with their greatest diameters perpendicular to the surface, 

 and ajnple intercellular spaces communicated with the external air through 

 the stonmta {Fig. 10). The stomata were much more abundant per 

 unit area on these organs than on the leaves or bracts near the in- 



