IO PHYSIOLOGY. 



Young or growing parts of any one of various plants — the petioles 

 of young leaves, or young stems of growing plants — are suitable 

 for study. Tissue from the pith of corn (Zea mays) in young 



shoots just back of the 

 growing point or quite 

 near the joints of older but 

 growing corn stalks fur- 

 nishes excellent material. 

 *ig. 9. 



Cyciosis in niteiia. If we should place part 



of the stem of this plant under the microscope we should find 

 it too opaque for observation of the interior of the cells. This 

 is one striking difference which we note as we pass from the low 

 and simple plants to the higher and more complex ones ; not 

 only in general is there an increase of size, but also in general 

 an increase in thickness of the parts. The cells, instead of lying 

 end to end or side by side, are massed together so that the parts 

 are quite opaque. In order to study the interior of the plant 

 we have selected it must be cut into such thin layers that the 

 light will pass readily through them. 



For this purpose we section the tissue selected by making with 

 a razor, or other very sharp knife, very thin slices of it. These 

 are mounted in water in the usual way for microscopic study. In 

 this section we notice that the cells are polygonal in form. 

 This is brought about by mutual pressure of all the cells. The 

 granular protoplasm is seen to form a layer just inside the wall, 

 which is connected with the nuclear layer by radiating strands 

 of the same substance. The nucleus does not always lie at the 

 middle of the cell, but often is near one side. If we now kill 

 with alcohol and treat with iodine the characteristic yellowish- 

 brown color appears. So we conclude here also that this sub- 

 stance is identical with the living matter in the other very differ- 

 ent plants which we have studied. 



23. Movement of protoplasm in the higher plants. — Cer- 

 tain parts of the higher plants are suitable objects for the study 

 of the so-called streaming movement of protoplasm, especially 

 the delicate hairs, or thread-like outgrowths, such as the silk of 



