CHLOROPHYLL FORMATION" 429 



the latter, Bogorad reported a ratio of 2.4 to 1. Protochlorophyll has 

 been detected in dark-grown seedlings of Larix curopaea and Thuja 

 occidentalis by Lubimenko (1928) and in P. coultcri and P. jeffreyi by 

 Smith and Koski (1947-1948). In the two last-named plants the ratio of 

 protochlorophyll to chlorophyll a is about 1 to 50. 



Although the cotyledons of conifers are green when grown in the dark, 

 new leaves grown on mature branches and saplings placed in the dark 

 are almost completely devoid of chlorophyll (Boehm, 1859; Frank, 1870, 

 cited by Stahl, 1909; Lubimenko, 1926; Smith and Koski, 1947-1948). 

 Whatever chlorophyll they contain is a mixture of chlorophylls a and b 

 (Smith and Koski, 1947-1948). They contain protochlorophyll (Liro, 

 1911; Smith and Koski, 1947-1948). These etiolated needles green only 

 very slowly when placed in diffuse daylight at favorable temperatures 

 (Lubimenko, 1926; Smith and Koski, 1947-1948). 



Greening in the dark depends on the temperature. Boehm (1863) 

 found that seeds of P. pinea held at room temperature long enough to start 

 germination when placed in the dark at 5°-7° Reaumur were completely 

 etiolated. The species differ in their response to temperature: some are 

 completely etiolated, whereas others become slightly green when grown 

 at low temperatures. They green almost universally in the light at these 

 same low temperatures (Boehm, 1865; Burgerstein, 1900). Bogorad 

 (1950a) has shown that the quantity of chlorophyll accumulated in com- 

 plete seedlings of P. jeffreyi in the dark at 34° or 37°C is much less than 

 at 23.5°C. 



Schmidt (1924) determined that the red-to-green part of the visible 

 spectrum caused greening in P. silvestri embryos much more readily than 

 the green-to-violet portion did. 



There are a large number of other plants that green in the dark for 

 which only fragmentary data concerning their physiological behavior are 

 available. For information on these plants, the original articles must be 

 consulted (Bittner, 1905; Liro, 1911; Schimper, 1885; Burgerstein, 1900; 

 Lubimenko, 1926, 1928). 



8. USE OF CHLOROPHYLL MUTANTS 



Frequently, among the higher plants, individuals appear which are 

 abnormal in respect to their chlorophyll: some plants are completely 

 white, some are yellow, and some possess bizarre variegated patterns. 

 These chlorophyll mutants furnish material that can be of service in deter- 

 mining the processes involved in the biosynthesis of chlorophyll and in its 

 accumulation. 



Corn, for example, possesses over a hundred specific genetic factors 

 affecting chlorophyll (cf. Emerson et al., 1935; Demerec, 1935). Several 

 of the chlorophyll-deficient mutants of corn have been examined in order 



