930 



SCIENCE. 



[N. S. Vol. XVI. No. 415. 



to a derivative of chlorophyll Avhich has 

 been named phyllopoi-phyrhi. The two 

 pigments are almost identical in their per- 

 centage composition, the hsematoporphyrin 

 containing a little more oxygen than the 

 other. Both seem to be derivatives of 

 pyrrol. The most striking similarity be- 

 tween them is their absorption spectra, 

 their ethereal solutions both showing nine 

 bands of identical width and depth, those 

 of hffimatoporphyrin being a little more 

 towards the red end of the spectrum. 

 Their solutions in alcohol and ether show 

 the same color and the same fluorescence. 

 Though they differ in certain other re- 

 spects, notably the facility with which they 

 form crystals, it is impossible to deny that 

 a close relationship seems probable. If 

 this is established we may by analogy per- 

 haps learn something about the part played 

 by iron in the action of the chloroplast, 

 which so far has proved as obscure as the 

 relation of the metal to the pigment. It 

 is very suggestive to recall the resemblances 

 between the two pigments, the one playing 

 so prominent a part in animal, the other 

 in vegetable life. Both are associated with 

 a stroma of proteid, or possibly protoplas- 

 mic, nature, in which a solution of the pig- 

 ment is retained, apparently after the fash- 

 ion of a sponge. Both are concerned in 

 metabolic processes in which gaseous inter- 

 changes play a prominent part. Both are 

 in some way dependent on the presence of 

 iron for their individuality, even if iron 

 is not actually present in the molecule of 

 both. The iron being removed, the deriva- 

 tives which are foixnd are almost identical. 

 Further researches may throw a light on 

 this curious relationship, perhaps showing 

 that chlorophyll may enter into a combina- 

 tion with carbon dioxide as hfematin does 

 with oxygen. Such a combination might 

 well be the precursor of the decomposition 

 of the carbon dioxide which has been 

 already spoken of. 



We meet with another pigment in many 

 plants, the physiological significance of 

 which has in recent years begun to attract 

 some attention. This is the red coloring 

 matter, anthocyan, apparently related to 

 the tannins, which is developed especially 

 in the young leaves of shade-loving plants 

 when they become exposed to illumination 

 exceeding the intensity which they nor- 

 mally encounter. The formation of this 

 pigment is greatest in tropical plants, where 

 it is found usually in the epidermis of the 

 young leaves, though in some cases it ex- 

 tends to the mesophyll as well. The pig- 

 ment seems in some way to be supplemen- 

 tary to chlorophyll, for its absorption 

 spectrum shows that it allows all the rays 

 useful in photosynthesis to pass through 

 it. It is unlikely that it takes any share 

 in photosynthesis. Several theories have 

 been advanced to explain its presence; it 

 may be simply to protect the delicate cells 

 from the destructive action of too intense 

 light, or to avert the evil of overheating 

 from the solar rays. It has been suggested 

 that certain rays hinder the translocation 

 of starch, and that the pigment shields the 

 cells from the incidence of such rays. 

 Again the view has been advanced that the 

 red color is important in accelerating the 

 development of diastase from its antecedent 

 zymogen, which has been found to take 

 place under the influence of the rays of a 

 certain region of the spectrum. Wliile all 

 these views have been advanced, however, 

 there is little positive information bearing 

 upon either the formation or the function 

 of the pigment. 



Very little progress has been made with 

 the problem of the construction of proteid 

 matter in the plant, which still confronts 

 us. "The question of its relation to the 

 mechanism of photosynthesis has received 

 some attention without leading to any satis- 

 factory conclusion. Winogradski 's success 

 in cultivating the nitrate bacteria upon 



