116 PHYSIOLOGY OF NUTRITION. 



I have observed the behaviour in polarised light of a whole 

 series of different kinds of starch grains ; potato starch gave the 

 most beautiful figures of all. We can no longer retain the view 

 that the micella? of starch grains, and similar organised plant 

 structures, are of the nature of optically biaxial crystals. The 

 characteristic behaviour of organised plant structures in polarised 

 light must be otherwise explained. 4 I do not, however, as I have 

 already emphasised elsewhere, reject the theory that organised 

 plant structures consist of micella. 5 



1 See H. v. Mohl, Botan. Zeitung, 1858, p. 1. 



2 See Nageli, Sitzungsberichte d. Akadem. d. Wiss. zu Miinchen, 1862, Bd. 1, 

 p. 311. 



3 See detailed account in Nageli and Schwendener's Microscope. 



4 See Strasburger, Ban und Wachsthum d. Zellhaute, 1882, p. 208 ; and Zim- 

 mermann, Berichte d. Deutschen botan. Gesellschaft, Bd. 2, p. xvii. 



5 See Detmer, Lehrbuch der Pflamenphysiologie, 1883, p. 71. 



46. The Protoplasmic Structures of Plant Cells. 



All the albuminous and organised constituents of the cell con- 

 tents are to be regarded as protoplasmic structures (the living 

 protoplasm proper, the nuclei, leucoplasts, and the protein grains, 

 etc.). The chlorophyll bodies have already been discussed in 5, 

 and we shall return later to other protoplasmic structures impreg- 

 nated with pigments. 



The appearance which the protoplasm (cytoplasm) of the cells 

 presents under the microscope is essentially dependent on the 

 number and size of the vacuoles filled with cell-sap which are 

 present in it. The presence of many small vacuoles in the plasma 

 gives it a foamy appearance ; while the protoplasm of many cells, 

 especially of mature ones, exhibits a single continuous sap cavity, 

 such as is represented in Fig, 5, p. 18, and in Fig. 38. We mount 

 in a drop of water, without special preparation, young leaves from 

 the end bud of an Elodea, and examine under the microscope. The 

 parietal layer of protoplasm, lining the inside of the cell membrane 

 of each cell, is easily made out, as also the mass of protoplasm 

 collected round the nucleus. These two are connected by threads 

 of protoplasm which traverse the vacuole of the cell. In the 

 protoplasm numerous chlorophyll bodies are readily seen. The 

 staminal hairs of Tradescantia are made up of single rows of cells 

 containing a violet cell-sap. These cells are similar in their 



