90 SUMMARY OF CURRENT RESEARCHES RELATING TO 



during the whole of their existence; (2) at first colourless, then 

 forming chlorophyll, which remains till the death of the cell ; 

 (3) colourless and forming chlorophyll, which afterwards passes over 

 into santhophyll ; (4) colourless, producing xanthophyll directly 

 sooner or later ; (5) coloured by xanthophyll during the whole of 

 their existence. 



The chromoplasts of flowers may be classified as follows : — A. In 

 the last stage of development round, or (in the epidermis) more or 

 less angular from mutual pressure, never fusiform, (a) They produce 

 comparatively little xanthophyll, and appear at last more or less 

 flat and irregularly filled with vacuoles ; xanthophyll light yellow. 

 (h) They produce comparatively little xanthophyll, and contain till the 

 end a great quantity of starch ; xanthophyll light yellow, (c) They 

 produce a comparatively large quantity of xanthophyll, and are finally 

 more spherical : a. with none or very few vacuoles, and xanthophyll 

 reddish yellow ; /3. xanthophyll light yellow, (d) They produce a 

 comparatively large quantity of xanthophyll, which finally lies within 

 the protoplasm in a granular form. B. They finally become fusiform 

 from the tendency of the xanthophyll to crystallize ; xanthophyll 

 usually dark or reddish yellow. C. They produce crystalloids in 

 or on them, by which they are more or less stretched. Of each of 

 these types, between which there are transitional forms, the author 

 cites examples. 



Formation and Resorption of Cystoliths.* — According to J. 

 Chareyre, the reserve-materials of the Urticinese and Acanthaceae 

 consist of aleurone-grains, each of which contains a globoid ; Acanthus 

 and Mexacentris also contain starch. The globoids which constitute 

 the calcareous reserve-materials of the seed disappear more com- 

 pletely if the plant is cultivated in pure sand than in limestone or 

 ordinary soil ; but they do not contribute to the formation of cysto- 

 liths. In pure silica the pedicel only of the cystoliths is formed. 

 In darkness only rudimentary cystoliths are produced. 



In the Acanthacese etiolation and death produce no effect on the 

 cystoliths ; but in Ficus elastica the calcium disappears in darkness 

 after about fourteen days. The resorption of the calcium carbonate 

 does not result from its passing over into the alkaline carbonate. 

 Under normal conditions, the cystoliths are formed again in a 

 month or six weeks. Calcium oxalate behaves in the same way. In 

 etiolated leaves of Ficus, sulphuric acid produces a larger quantity of 

 crystals of gypsum than in normal leaves. 



Function of Organic Acids in Plants.f — W. Detmer regards the 

 organic acids as having a very important function as the chief pro- 

 moters of osmose, and consequently of the turgidity of the cell. The 

 conversion of starch into sugar is also greatly dependent on the 

 presence or absence of free acids; the presence of carbonic acid and 

 of small quantities of hydrochloric, nitric, phosphoric, citric, and oxalic 



* Comptes Eendus, xcvi. (1883) pp. 1594-6. Cf. this Journal, iii. (1883) 

 p. 389. 



t SB. Jenaisch. Gesell. Med. u. Naturw., 1883, pp. 47-9. 



