120 



PHYSIOLOGY OF NUTRITION. 



The starch-forming corpuscles, leucoplasts, have a special 

 interest for us. Their function, as Schimper first demonstrated, 4 

 is the regeneration of starch grains from dissolved carbohydrates 

 which are in migration, or have already passed over into 

 receptacles for reserve material. The largest and most beautiful 

 starch-forming corpuscles with which we are acquainted occur in 

 the pseudo-tubers of Phajus grandifolius, one of the Orchidacere. 

 For examination we select a not too old tuber, halve it, and pre- 

 pare from the crown thin longitudinal sections including the green 

 surface of the tuber. I have satisfied myself that it is best to 



transfer the sections rapidly to 

 concentrated Picric acid, and ex- 

 amine them in this. The starch- 

 forming corpuscles of the cells of 

 the inner parts of the sections are 

 colourless; towards the outside 

 the starch-formers certainly be- 



IV j$ come larger, but their proto- 



I/S plasmic matrix is impregnated 



v l\ with chlorophyll. The leucoplasts, 



when seen in profile (see Fig. 39), 

 appear rod-shaped. They have 

 assumed a yellowish colour owing 

 to the treatment with the Picric 

 acid, while the larger or smaller 

 starch grains seated on them 

 remain unstained. 

 We now proceed to investigate the protoplasmic structures of 

 resting organs. .Above all, we are interested in the forms in which 

 reserve proteid materials occur in seeds. We first of all take for 

 examination a lupin seed, halve it, moisten the cut surface of the 

 cotyledons, and examine delicate sections in water. We find in 

 the cells numerous small aleurone or protein grains, lying closely 

 packed together, which have become somewhat changed in form 

 under the influence of the water. If preparations are examined 

 in glycerine, the unaltered protein grains appear as highly re- 

 fringent bodies, which at first sight look like small starch grains. 

 The aleurone grains in the cells are imbedded in a protoplasmic 

 matrix. Very beautifully developed, large protein grains, em- 

 bedded in a fatty matrix, occur in the endosperm cells of the seeds 

 of Ricinus. Sections of the tissue are easily prepared, and may 



FIG. 39. Phajus grandifolius, starch 

 formers from the tubes. A, C, D and E. 

 seen from the side ; B, from above. 

 Magn. 510. (After Strasburger.) 



