1873.] 



Comparative Vegetable Chromatology. 



473 



There is a decided indication of the same fact in the case of the lichno- 

 xanthine in Peltigera, but scarcely sufficient to prove it conclusively. 



The above examples must be looked upon merely as indications of 

 what may be done ; but they will, I trust, be sufficient to show that the 

 study of the relative amount of the various colouring-matters found in 

 the same plant, under different conditions, is likely to throw much light 

 on certain questions connected with vegetable physiology. 



Comparison of different Plants. 



Though I have examined a good many of the principal classes of plants, 

 yet there are many that I have not yet been able to procure in a proper 

 state for examination. It is also desirable to investigate more fully 

 certain of the lower classes of animals, especially the sponges and polyps, 

 and to ascertain the laws regulating the distribution of some of the colour- 

 less constituents of plants, though that would require entirely different 

 methods of study. Residing, as I do, inland has increased my difficulties, 

 and I have been obliged to rely on what I could learn during a temporary 

 residence in Devonshire, and from material subsequently sent to me by 

 Dr. Baker of Dawlish, Mr. Charles Horner of Mortlake, and other kind 

 friends. At the same time, being able to spend several hours every day 

 in the open country, at all seasons of the year, has been of great value 

 in studying other parts of my subject. 



In the present state of the question there is some difficulty in deciding 

 what general principles should be adopted in attemptiug to arrange the 

 various classes in a natural order, in accordance with the nature or re- 

 lative amount of the colouring-matters. For example, whether they 

 should be arranged in a single linear series, or in two or more parallel or 

 divergent groups. This difficulty is partly due to the existence of sudden 

 gaps, not yet filled up by intermediate examples, so that the true con- 

 nexion is not quite apparent. I have constructed a table, representing 

 what is so far known ; but I think it better not to publish it until more 

 complete — only to describe some of the principal conclusions deduced 

 from it. 



Connexion of the different Groups of Algce. 



Perhaps I cannot choose a better illustration than that furnished by 

 the different groups of Alga? — the olive, the red, and the green. They 

 contain at least twelve different colouring-matters, distributed very 

 differently, in such a manner as to connect, and yet to distinguish, the 

 different groups very characteristicalty. I have not yet made any ac- 

 curate quantitative analyses, and therefore express the relative amount 

 of the various substances by the following signs : — 



A relatively large quantity # 



A relatively moderate quantity -f 



A relatively small quantity 



