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Elementary Plant Physiology. 



may empty the cells of the leaf of soluble contents, and then 

 the starch is reconverted into a soluble form. This is accom- 

 plished by the action of diastase, as demonstrated in §iii. 

 The main channels of conduction of food material are found 

 to be the elongated elements in the phloem, principally the 

 sieve and companion cells. These cells are adapted to the 

 diffusion of solutions much more quickly than the neighbor- 

 ing cells of shorter axes, such as the sheath cells, which were 

 once supposed to carry on this function. 



ii6. Translocation of carbohydrates from leaves. 

 — Expose any convenient living 

 specimen to a strong sunlight during 

 an entire day, and examine the tis- 

 sues for starch in the evening. If 

 the leaves are richly loaded with 

 this substance, suitable conditions 

 for the test are found. Cut off a 

 few of the leaves, and place in a 

 moist chamber. Set the plant and 

 the moist chamber in a dark room, 

 and allow them to remain until the 

 following day at lo a.m. Now ex- 

 amine leaves from the plant, and 

 those that have lain in the dark chamber, for starch. In 

 what way may the difference in amount in the severed 

 leaves and those still remaining attached to the plant be 

 accounted for ? It would be well to carefully cut the main 

 veins of one of the leaves attached to the plant before being 

 placed in the dark chamber, in such manner as to break 

 the conducting cells around them, and note what effect the 

 operation has upon the translocation of starch from the leaf. 

 Definite results may not always be seen, however. 



117. Excretion of nectar. — Examine a number of 

 plants that are being visited by honey-gathering animals, and 



Fig. 78. — Transverse section 

 of nectary oi A loe vera . c, cu- 

 ticle. After Schniewind-Thies. 



