CHAPTER XI 



INTERRELATIONS BETWEEN DIFFERENT PARTS OF 

 THE PLANTS. VEGETATIVE PROPAGATION 



91. The Plant as a Unit Organism. Correlation. — Separate 

 parts of the plant possess a considerable degree of independence, 

 much greater than the separate parts of the animal organism.s. 

 The well-known method of propagation by means of cuttings, 

 which will be discussed in detail further on, shows that a small 

 section of a branch of a plant, provided that it carries a bud, will 

 frequently reproduce all the rest of the organs of the plant. In 

 some plants, even small bits of a leaf, stem, or root when sepa- 

 rated from the mother organism may form a new growing point 

 and reproduce the whole plant. There are reasons to suppose 

 that any undifferentiated cell of a higher plant should be capable 

 of regenerating the whole organism. If this does not always 

 occur, the chief reason is that all the conditions that are necessary 

 for regeneration and that are not yet known have not been 

 fulfilled. 



This independence of the separate parts of the plant serves as a 

 basis for some of the methods of study of physiological processes. 

 In the discussion of respiration, photosynthesis, transpiration, 

 and other functions of the plant, it has been seen that very often 

 they are studied on separate branches and even leaves, the sup- 

 position being that the parts of the plant represent the whole 

 and that there is no substantial difference in the processes 

 occurring therein. This has led many to the conviction that 

 the plant does not represent a united whole but resembles a 

 colony of separate parts very httle connected with each other. 



This concept is quite erroneous. In spite of the clearly 

 understood ability of the parts of plants to continue an inde- 

 pendent existence after separation, the plant represents a unit 

 structure, all the parts of which are reciprocally coordinated and 

 produce a certain influence on each other. Cases of such a 

 coordination have already been cited. For instance, in the dis- 

 cussion of the water balance of plants, it has been shown that 



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