H. BOTANY AND HORTICULTURE. 309 



developed, its color, combined with this yellow, gives rise to 

 scarlet or red. In many cases, however, the chlorophyl does 

 not disappear, but is changed into the dark olive modifica- 

 tion, easily prepared artificially by the action of acids on the 

 more green shades ; and when this is present, only dull and 

 unattractive tints can be produced. We may thus easily un- 

 derstand why the special tints of early autumn are yellows 

 and reds, or dull and dark greens. In these changes the va- 

 rious pale-yellow substances of the chrysotannin group re- 

 main comparatively unaltered, and even sometimes increase 

 in quantity, but they soon pass into the much darker red- 

 browns of the phaiophyl group, while the erythrophyl fades, 

 and thus later in the autumn the most striking tints are the 

 brighter or the duller browns, characteristic of the different 

 kinds of plants or trees. 



As far as we are able to judge from the various facts de- 

 scribed above, we must look, according to Mr. Sorby, upon the 

 more characteristic tints of the foliage of early spring as evi- 

 dence of the. not yet matured vital powers of the plant. In 

 summer the deeper and clearer greens are evidence of full 

 vigor and high vitality, which not only resist, but also actu- 

 ally overcome the powerful affinity of oxygen. Later in the 

 season the vital powers are diminished, and partial changes 

 occur ; but the affinity of the oxygen of the atmosphere is 

 nearly balanced by the weakened, though not destroyed vi- 

 tality. At this stage the beautiful red and yellow tints are 

 developed which produce so fine an effect in certain kinds of 

 scenery. Then comes more complete death, when the affinity 

 of oxygen acts without any opposition, and the various brown 

 tints of later autumn make their appearance, due to changes 

 which we can imitate in our experiments with dead com- 

 pounds. 12 A, August 31, 342. 



CLEARING BJEAN OF IXDIA. 



Among other vegetable productions of India is a species 

 of Strychnos, known there as the clearing nut, the dried seeds 

 of which are used to a considerable extent for the purpose of 

 clearing muddy water. For this purpose one of the nuts is 

 usually rubbed hard for a short time round the inside of the 

 earthen pot ; the water afterward is poured into it and left to 

 settle, the impurities soon subsiding, and the water being left 



