THE FOOD OF THE PLANT 67 



4. The only consistent explanation of these facts is 

 that the food-material, elaborated in the leaves, passes 

 through the plant in the tissue outside the wood. Assum- 

 ing this, the facts recorded can be explained thus : 



In plant a the leaves continue to unfold after " ring- 

 ing," as the water supply has not been checked ; the 

 expanded leaves then manufacture starch; the starch 

 is converted into sugar; it is then further combined 

 with the substances from the watery solutions coming 

 from the soil. The final product of this assimilation 

 then passes down the stem until it is stopped by the 

 cut ring. As a result no further manufactured food- 

 stuff ever reaches the root ; the root is unable to per- 

 form its functions properly and to grow with the growth 

 of the shoot above ; the plant ultimately dies as a 

 result of the starvation of the root. 



In plant h the initial stages are similar to those of 

 plant a, but later the root is kept from starving because 

 nourishment is sent to it by the new leaves that grow 

 helow the ring. The root-development, which thus 

 takes place, is not sufficient to maintain proper develop- 

 ment of the main shoot above the ring ; as a result of 

 this the leaves of the main shoot cannot form their 

 cork-layers and so they droop, but do not fall off ; but 

 the root-development is sufficient to keep the plant 

 alive for a considerable time and to enable the shoot 

 to form its winter resting buds. 



Since this explanation fits all the observed facts, it 

 may be concluded that the food-inaterial manufactured 

 in the leaves passes to different parts of the plant 

 through the tissues outside the wood. 



Comparison of the Feeding-process in Animals and 

 Plants. — The feeding-process in plants and animals can 

 now be compared. 



Animals are unable to utilise, as food, the constitu- 

 ents of the air and the soil. They cannot build up 

 starch from carbon-dioxide and water. They must, 

 therefore, feed on the starch and sugars that the plants 

 have already manufactured. 



