Guilliermond - Atkinson 



— 46 



Cytoplasm 



and become green to be transformed into chloroplasts (called 

 chloroplastids by Schimper). In flowers and fruits, Schimper 

 has shown that the carotinoids, xanthophyll and carotin, always 

 form in plastids which he calls chromoplastids but which we shall 

 call chromoplasts. These may either form directly by transforma- 

 tion of small leucoplasts, which may or may not have previously 

 formed starch, or they may, in other cases, arise by a metamorpho- 

 sis of chloroplasts whose chlorophyll disappears and is then re- 

 placed by a carotinoid. Pigment may appear in the chromoplast 

 either in the amorphous or in the crystalline state. In the former, 

 which is always the case when the pigment is xanthophyll, the 

 chromoplasts affect the same globular or lenticular form as the 

 chloroplasts. In the crystalline state, which is frequently the case 

 when the pigment is carotin, the crystals are contained in variable 

 number in the chromoplasts, and usually take the form of needles 



Fig. 15. — Inclusions of the plastids. 1, chloro- 

 plasts in epidermal cells of Hedera leaves. 2, chlo- 

 roplasts in palisade parenchyma of leaves of Aehy- 

 ranthes Verschaffelti. 3, leucoplasts in young buds 

 of Carina Warszetvickzii. A, starch; C, protein crys- 

 talloids. 4, chromoplasts in the flower of Neottia 

 Nidus-avis. C, carotinoid crystal; P, protein crys- 

 talloid. (After Schimper). 



delicately curved in hooks, spirals or slender rods. Sometimes they 

 appear as triangular or rectangular tables, hollow tubes, or spiral 

 ribbons. They are all rhomboidal prisms. The crystals are ar- 

 ranged in parallel or divergent bundles in the chromoplast which, 

 following the contours of the crystal, takes on most varied aspects : 

 rods, spindles, triangles. In some cases, as in the carrot root, the 

 crystals, when once formed, have worn out the greater part of the 

 substance of the chromoplast which made them, and appear either 

 free in the cytoplasm or simply surrounded by a very thin and 

 barely perceptible plastidial envelope. In other cases, there may 

 be formed in chromoplasts not enclosing crystalline pigments, sev- 

 eral needle-shaped crystalloids of protein which bring about an 

 elongation of the plastid and give to it the shape of a spindle or 

 rod. It even happens that chloroplasts contain both pigment crys- 

 tals and protein crystalloids as, for example, in the fruit of Loni- 

 cera xylosteum, in which the chromoplasts are pear-shaped. The 

 pigment is distributed m the thicker portion of the chromoplast 

 as small needle-shaped crystals, and a protein crystalloid occupies 

 the long axis of the chromoplast and spins out at one of its extremi- 

 ties in the shape of a tenuous appendage. (Figs. 14-17). 



