560 DR. A. J. EWART ON ASSIMILATORY INHIBITION. 
upper leaves not longer than 3 to $ em. may remain living for 
1-2 weeks, but have lost the power of turning green. This is 
generally the case with the basal simple leaves in such plants. 
If one of the cotyledons be removed from seedlings in which 
the plumule is but little developed, the plants remain small and 
the etiolated leaves retain their power of recovering and turning 
green in light as long as plants with both cotyledons do. If the 
young seedling has only one cotyledon, the deficient supply of 
nutriment causes the formation of a smaller plant, and the seed- 
ling is not starved any more rapidly than one with two cotyledons 
is. If, however, the seedling stems be a foot or so long when 
one cotyledon is removed, a marked difference is observed, 
although the plants do not increase nearly so much in length as 
seedlings with both cotyledons. The etiolated leaves on such 
plants lose the power of turning green when brought into light 
in from š to 2 the time that plants with both cotyledons do. If 
both cotyledons are removed the effect is still more quickly pro- 
duced, but the entire plant in such cases is very apt to die. 
Etiolated seedling plants (stems 12-15 cm.) of Vicia Faba gave 
similar results :— 
(a) Cotyledons removed. Plants cease to grow. After 1 week in darkness 
at 25° C., then in light, remain living for several days, but the young 
yellow leaves do not turn green and the plant slowly dies. 
(b) š of cotyledons removed. Plants grow, but only slowly. After 2 weeks 
in darkness same as in (a). 
(c) Cotyledons normal. After 2 weeks in darkness, then in light, all the 
leaves turn green, stems twice as long as in (b). After 4 weeks in dark- 
ness the power of recovering and turning green in the light is lost. 
It is by no means always the case that etiolated parts show a 
power of evolving oxygen in light. Thus the secondary foliage- 
leaves of Cucurbita and Helianthus and the compound leaves of 
Phaseolus, developed in darkness on the seedlings, do not show 
any power of assimilation. This is here very evidently due to 
the lack of nourishment inhibiting or interfering with the 
formation of etiolin and the development of, and attainment of 
functional activity by, the chloroplastids. 
In certain Gramine the leaves of seedling plants developed in 
darkness never attain any power of assimilation. 
