ZOOLOGY AND BOTANY, MICROSCOPY, ETC. (541 



The leucoplasts arc usually globular quite colourless structures, 

 often considerably more refringent than the surrounding protoplasm. 

 In a number of Angiosperms the chroinatophores contain protein- 

 crystals, which are isodiametric, tabular, or prismatic. The chroma- 

 tojmores of many Algae, and those of Antlioceros, contain pyrenoids, 

 one or more buried in the matrix of the chromatophore, like nucleoli 

 in the nucleus. Except in Porphyridium cruentum (Palmetto, omenta) 

 they are always colourless, and of a more or less delicate reticulate 

 structure. They are segments of the chroinatophores in which a 

 peculiar nuclein-like substance is imbedded ; they may increase by 

 division or by new-formation. 



In many flowers and fruits the chromoplasts have a crystalline 

 appearance, from containing crystalline substances which are either 

 albuminoids or pigments ; or both may occur in the same chromoplast. 

 The two kinds are distinguished by their different colour, their dif- 

 ferent behaviour to reagents, difference in form and in the degree of 

 double refraction, and by the pigment-crystals being always strongly 

 pleochroitic (not dichroitic). But in most cases the pigment of the 

 chromoplasts is not crystalline ; it does not then permeate the 

 protoplasm-strings, but is contained in small vacuoles in a fluid or 

 semi-fluid, or sometimes a solid condition. The chromoplasts are 

 always formed by the transformation of other chromoplasts, cither 

 leucoplasts or more often chloroplasts. 



Chloroplasts have probably the same structure as chromoplasts ; 

 they consist of a colourless stroma with numerous vacuoles filled by 

 a green semi-fluid substance. The chloroplasts of all Pteridophyta 

 and Phanerogamia contain granules, termed by Strasburger cltromato- 

 somes ; these are especially well marked in the prothallia of ferns. 

 The same is the case with all the higher Muscineae ; while in 

 Antlioceros and in all Alga3 the chloroplasts are of a homogeneous 

 green colour, or only very finely punctated, but not granular. In 

 many green Algae the pigment is not uniformly distributed, but is 

 chiefly accumulated in the marginal parts of the chroinatophores. 



It has long been known that in some cases — the cotyledons of 

 Conifers and the fronds of ferns — chlorophyll may be formed quite 

 independently of light ; the author believes that this is generally the 

 case with Muscineae, Characeae, and Algae, and partially also with the 

 Pteridophyta. The chlorophyll-pigment is destroyed by intense 

 light. 



The chromatophores of flowering plants contain oil ; and this 

 occurs in all organs, especially in persistent leaves. The various 

 substances produced from the chromatophores are never products of 

 the cell-protoplasm or nucleus ; and the chemical changes which take 

 place in the chromatoplasm are also different from those in the 

 cytoplasm and nucleoplasm. The chlorophyll and starch are produced 

 entirely by the chromatophores. 



The chromatophores are invariably enclosed in at. least a thin 

 coating of protoplasm. The arrangement of the chromatophores in 

 the cell is sometimes altogether irregular ; more often it is constant 

 and in definite relationship to the cell-contents. In cells which do 



Ser. 2.— Vol. VI. 2 U 



