160 



THE CELL 



as constantly as the nucleus, and possess great functional independ- 

 ence. They are of great importance in the nutrition of plants, 

 for the whole process of assimilation and the formation of starch 

 takes place in them (Meyer V. 9-11). 



Trophoplasts are small bodies, which are generally either 

 globular or oval in shape ; they are composed of a substance very 

 similar to and yet distinct from protoplasm. They are easily de- 

 stroyed, whilst the preparation is being made, by either water or 

 reagents, and are most successfully fixed by means of tincture of 

 iodine, or concentrated picric acid. They acquire a steely blue 

 coloration in nigrosin, and thus stand out clearly from the proto- 

 plasmic body. They often occur in great numbers in the cell, and 

 may actively change their form. According to the investigations 

 of Schmitz (V. 29), Schimper (V. 27, 28), and Meyer (V. 9-11), 

 trophoplasts are not direct new formations in the protoplasm, but 

 on the contrary reproduce themselves, like nuclei, from time to 

 time by division. According to this conception, all the tropho- 

 plasts in the generations of cells which spring from the original 

 vegetable egg cell are derived from those trophoplasts which 

 were originally present. 



Various kinds of trophoplasts may occur, fulfilling various 

 functions ; these are distinguished as starch-forming corpuscles, as 



chlorophyll corpuscles, and 



FIG. 67. Phajus grandi/olius, amylo- 

 plat-ts from the tuber(after Strasburger, 

 Botanitches Prakticum, Fig. 30) : A, C, 

 U, nnd Bare seen from the side, B from 

 above, E is coloured green. ( x 540.) 



pigment-granules (amylo- or leuco- 

 plasts, chloroplasts, chromoplasts). 

 Most starch-forming corpuscles 

 (amyloplasts) (Fig. 67) occur 

 in the non- assimilating cells of 

 young plant organs, and in all 

 underground portions, as also in 

 stems and petioles. In the 

 pseudo-tubers of Phajus grandi- 

 folius, which are especially suitable 

 for investigation, they form, when 

 viewed on the flat, ellipsoidal 

 finely granular discs, whilst when 

 viewed from the side they look 

 like small rodlets ; these when 

 treated with picro-nigrosin stain a 

 steely blue colour, and so stand 

 out clearly from the surrounding 

 protoplasm. On one of the flat 



