HISTOLOGY OF HIGHER PLANTS 



61 



activities, stores most of it up in the complex chemical compounds 

 which it manufactures. 



Nevertheless, though the degree of histological differentiation 

 is not nearly so high as it is in the higher animals, we find in 

 the higher plants also a considerable variety of cells and tissues, 

 derived, as we have already pointed out, from the dermatogen, 

 periblem and plerome of the embryo. 



We may illustrate this point by a study of some of the cells 

 and tissues which occur in the well-known spiderwort of our 

 gardens, Tradescantia virginica. If we examine the flowers of 

 this plant we shall find that the stamens are covered with long 



FIG. 25.' Structure of a Hair from a Stamen of Tradescantia virginica. 



A. End of a hair as seen under a low power of the microscope. The hair is made up of 



a single row of cells. 



B. A single cell more highly magnified. 



c.w. cell-wall; nu. nucleus; p.u. primordial utricle; vac. vacuole filled with coloured 

 or colourless cell-sap. 



slender hairs. It will be convenient to make these hairs the 

 starting point of our inquiry. If we study them first under a low 

 magnifying power we shall see that each hair (Fig. 25, A) is 

 made up of a single row of cells, arranged like the beads in a 

 necklace ; most of the cells are elongated, but towards the apex 

 of the hair they become short and spherical. 



If we now concentrate our attention on one of the larger cells 

 and study it carefully under a moderately high power of the 

 microscope, we shall find that it exhibits the appearance shown 

 in Fig. 25, B. It measures about 0*27 mm. in length by 

 0*08 mm. in breadth and consists of a thin-walled bag filled 

 with living protoplasm. The wall (c.w.) is transparent and 

 colourless and is composed, as in Haematococcus, of cellulose. 



