THE CHLOROPLAST PIGMENTS 



473 



solution as well as of its effect upon 

 chlorophyll in the plant. 



The work of Oddo and Pollacci must be 

 considered in a review of this kind. 

 They found that corn, Datura, Solatium, 

 Euphorbia and asters grown in solutions 

 containing magnesium pyrrole-di-carboxy- 

 late were normal, while plants grown in a 

 •solution which did not contain this pyrrole 

 compound were chlorotic. When pyrrole 

 was present even in the absence of iron, 

 greening was observed. Referring to 

 Mamelis' work they believe that pyrrole 

 and magnesium are the factors which 

 determine the green coloration of plants. 

 In this connection it is interesting to note 

 that Kraybill in working on tomatoes 

 found that dried blood caused the plants to 

 be deeper green and more vigorous. One 

 cannot help wondering whether the blood 

 has been ammonified or whether the nitro- 

 gen has been absorbed while still in the 

 pyrrole form. We are forced to question 

 whether the following statement so often 

 found in the literature is correct : it is only 

 after decomposition and conversion into 

 ammonia and nitrates that the numerous 

 important organic nitrogen fertilizers are 

 to any practical extent valuable for plants. 

 Ciamician and Galizzi report that certain 

 pyrrole compounds are not toxic to plants, 

 while Emerson reports that pyrrole com- 

 pounds have been used in nutrient solu- 

 tions with varying success. Deuber's 

 work seems to show that the pyrrole com- 

 pound used by him is toxic to plants. 

 Just what the real situation is in regard to 

 pyrrole compounds would be difficult to 

 say from the small amount of work which 

 has been done upon the relation of pyrrole 

 to plant growth. In Deuber's work it is 

 interesting, however, to note the luxuriant 

 development of bacteria in the cultures 

 which contained the pyrrole compound. 

 Schreiner and Skinner studied the effect of 

 nitrogen compounds upon the growth of 



plants and paved the way for work which 

 at the present time offers much promise in 

 the realms of plant physiology. 



We are also led to wonder about the 

 factors which influence photosynthesis. 

 Just what are the limiting factors anyway? 

 Briggs and Irving conclude that the power 

 of photosynthesis lies behind the develop- 

 ment of chlorophyll. The photosynthetic 

 power of a leaf increases with age even 

 though there is no concurrent increase in 

 the chlorophyll content. Others believe 

 that there is an internal factor, inde- 

 pendent of chlorophyll and associated 

 with protoplasm, which controls the rate 

 of carbon assimilation. Since the assimi- 

 lation numbers arrived at by Willstatter 

 and Stoll are not constant this is very 

 strong evidence that chlorophyll is not the 

 all important factor in photosynthesis. 

 They believed that an enzyme limits 

 carbon assimilation. Even to this day 

 nobody has succeeded in bringing about 

 carbon assimilation by means of chloro- 

 phyll which has been isolated from the 

 leaf. 



This brings us to the factors which 

 influence the formation of chlorophyll. 

 Light, temperature, iron, mineral salts, 

 oxygen, carbohydrates and others seem to 

 be the factors which are stressed mostly 

 in our modern texts. It is very remark- 

 able that the element nitrogen does not 

 seem to be given a place as a possible 

 factor in chlorophyll formation. In one 

 of our most modern texts some such state- 

 ment as this is found: iron salts and 

 nitrates are regarded as favorable for 

 chlorophyll development. Others make 

 no mention of any possible relation be- 

 tween nitrogen and the green pigment. 

 Nitrogen has been considered more in 

 its relation to proteins. However, a few 

 have seen a possible relation of nitrogen to 

 the color of green plants. 



It was Ville who first showed that nitro- 



