204 



CHLOROPHYLL 



CHLOROSIS 



times to tinge the whole protoplasm of the cell 

 ( though never the cell sap ). Much more generally, 

 however, it is collected into definite bodies, the 

 so-called chlorophyll granules, or less frequently, as 

 in some of the lower algae, arranged in starlike 

 masses ( Zygnema ) or spiral bands ( Spirogyra ). A 

 brief immersion of the specimen in alcohol suffices 

 to dissolve out the chlorophyll, and leave the form 

 of the chlorophyll bodies unaltered ; and the solu- 

 tion may then be conveniently studied in a fresh 

 state, as it gradually fades on keeping. It is of a 

 deep rich green by transmitted, but of characteristic 

 deep red colour by reflected light ; in a word, is 

 highly fluorescent. The absorption-spectrum is 

 quite characteristic ; yet the complex nature of the 

 substance is strongly argued for on the ground of 

 the following experiment. Shake up the alcoholic 

 . solution with benzol, and when the two fluids have 

 had time to separate, we find the green to have 

 disappeared. The lighter alcohol above is now of a 

 strongly yellow hue, while the subjacent benzol is 

 of a distinctly bluish green. To these colouring 

 matters the names Xanthophyll and Cyanophyll are 

 commonly given. While their separate spectra are 

 quite characteristic, their combined spectrum seems 

 to restore that of chlorophyll. The latter sub- 

 stance resembles the blue-green colouring matter of 

 some of the lowest algae ( Oscillatoria, &c.), while 

 the yellow substance recalls that of many buds 

 and flowers. Others, however, maintain that these 

 substances are really the result of a destructive 

 decomposition of true chlorophyll ; while Gautier 

 has even prepared green needle-like crystals which 

 he regards as chlorophyll in a pure state. The 

 chemical composition of chlorophyll is also a matter 

 of considerable difficulty, botn on account of its 

 own easy decomposability, and its being necessarily 

 accompanied by other extractive substances ; thus 

 the question of the presence or absence of iron has 

 been much debated, a matter which seems to in- 

 dicate variability of composition. This is further 

 borne out by the labours of spectroscopists. Thus 

 in addition to the familiar well-defined analogous 

 colouring matters which characterise respectively 

 the blue-green algae, the brown and the red (see 

 SEAWEEDS), researches such as those of Sorby and 

 others seem to indicate a number of varieties too 

 numerous even for enumeration. This varietal 

 range, however, may best be approached after 

 considering the conditions in which chlorophyll is 

 formed. Of the chemical factors little can be said 

 save that the presence of iron in the soil seems to 

 be quite indispensable ; the physical conditions 

 are, however, simpler. 



A sufficient temperature is necessary to the for- 

 mation of chlorophyll ; for seedlings from 4 to 8 C. 

 being a minimum, while the process is said to take 

 place most rapidly, on the average, at about 35 C. 

 The most important condition is, however, the pres- 

 ence of light ; with rare exceptions, plants cannot 

 form any chlorophyll in darkness. The blanching 

 of celery or leeks is a familiar instance of this, or 

 conversely, the green coating acquired by a potato- 

 tuber where it happens to have been denuded of its 

 covering of earth. Shoots formed in darkness form 

 colouring matter indeed, but only of a pale-yellow 

 hue, the so-called etiolin ; after a very brief exposure 

 to light, especially if direct sunshine, chlorophyll 

 appears, apparently by direct transformation of the 

 former. The other colouring matters of plants 

 are sometimes in protoplasm granules (chromo- 

 plasts), but more frequently also in solution in the 

 sap ; and these frequently are present in such abund- 

 ance, especially in the epidermis, &c., as to mask 

 the chlorophyll altogether, as happens especially in 

 so many of our hothouse plants with decorative 

 leaves. The general tendency of research is to 

 indicate that all the phenomena of plant colour 



seem intimately connected with what we may term 

 the general life-history of chlorophyll. Thus the 

 yellows and reds of young shoots and leaves in 

 spring may be interpreted as having some relation 

 to the development of chlorophyll, if not absolutely 

 stages of the process ; while the same suggestion 

 arises with regard to the colouring matters of 

 flowers, which are similarly to be regarded as 

 imperfectly vegetative shoots, although in this case 

 through the onset of the reproductive function, 

 instead of merely by reason of immaturity. Finally 

 also with regard to the autumnal hues, in which 

 the chlorophyll pigment seems to be disintegrating 

 through colour-stages analogous to those of its 

 evolution in spring, or of its arrestment in the 

 flower. In favour of such a view evidence is forth- 

 coming from either end of the vegetable kingdom. 

 Thus Cienkowsky has shown that in the case of 

 certain unicellular algae, which like the common 

 Protococcus of rain-water, possess red pigment as- 

 well as green when passing into the resting stage, 

 the quantity of red may be increased in proportion 

 as autumnal conditions are reproduced by artificially 

 lowering the temperature, and vice versa. The 

 same experiment may be made with the common 

 Sempervivums, Sedums, &c. , whose leaves become 

 more or less red in autumn or winter ; those of 

 Thuja (Arbor Vitce] similarly become brownish, 

 but recover themselves in spring. Among almost 

 all cultivated plants, variegated varieties tend to- 

 arise, that is to say, we have certain cell -areas of 

 the leaf-parenchyma destitute of chlorophyll. The 

 conditions of this are quite obscure (see VARIE- 

 GATION) ; but it is noteworthy that this loss of 

 chlorophyll may also take place in lower plants, so- 

 that there is considerable ground for regarding 

 at least many apparent fungi as simply algae which 

 have degenerated in this respect through parasit- 

 ism. Phanerogamous parasites like Toothwort 

 (q.v. ) or Dodder (q.v. ) similarly become almost 

 completely blanched. 



Chlorophyll apparently identical with that of 

 green parts of plants, can be experimentally de- 

 monstrated in the tissues of certain animals ; and 

 although this has in many cases been shown to be 

 due to the presence of symbiotic algae (see SYM- 

 BIOSIS), there remain cases e.g. Hydra viridis y 

 &c., and at the very least Paramoecium viride, in. 

 which we have undeniably intrinsic chlorophyll, 

 and this of truly vegetable function. 



The development of our knowledge with respect- 

 to the functions of chlorophyll is still far from com- 

 plete, and may in any case be more conveniently 

 treated under LEAF and VEGETABLE PHYSIOLOGY 

 (q.v. ) ; suffice it therefore to state here the elemen- 

 tary and essential fact that its presence is in every 

 case constantly associated with the process of 

 assimilation, or elaboration of new products by help- 

 of the energy of sunlight, upon which the continued 

 nutrition of the green plant depends ; and of which 

 the formation of starch with decomposition of car- 

 bonic anhydride and disengagement of oxygen are 

 the most obvious chemical results. A fuller account 

 of the state of knowledge and opinion upon this 

 portion of the subject will be found in the articles, 

 referred to. 



Chlorops. See CORN INSECTS. 



Chloro'sis ( Gr. chloros, ' pale green ' ), a peculiar 

 form of anaemia or bloodlessness, common in young 

 women, and connected with the disorders incident 

 to the critical period of life. It has been called the 

 green sickness, from the peculiar dingy greenish- 

 yellow hue of the complexion ; the green colour, 

 however, is not always present. The disease is 

 attended with very great debility, and often with 

 breathlessness, palpitation, and other distressing 

 or even alarming symptoms. In a few cases it is. 



