26 



of the same plant they should, apart from slight differences 

 of nutrition, not only be all similar but actually of the 

 same constitution. It is true that bud variation does 

 occasionally arise in plants, but it is a comparatively rare 

 phenomenon, and consequently we find that as a rule 

 plants, raised by vegetative methods, maintain the char- 

 acter of the parents and do not show the sporting with 

 which one is familiar when raising plants from seed. The 

 purity of the strain is thus easily maintained by vegetative 

 propagation. 



Let us now examine some of nature's methods of 

 vegetative reproduction. In the first place, we have such 

 well-known examples as tubers which form the chief 

 method of propagation of the potato and of the Jerusalem 

 artichoke. A tuber is the swollen-up end of an under- 

 ground branch. This can be clearly seen by digging up 

 a young potato plant and following these subterranean 

 shoots from the parental stem to their tuberous tip. Both 

 the branch and also the tuber show the rudiments of 

 leaves, reduced to small scales and spirally arranged 

 round the potato. On an old potato the sickle-shaped 

 mark below each eye or lateral bud represents the insertion 

 of the leaf or leaf scar, and at one end of the potato where 

 these become more crowded together, we have the terminal 

 bud of the tuber. This is called the "rose" end. At the 

 opposite end we can generally find the scar or heel where 

 the branch of which the tuber is the dilated tip, was joined 

 to it. In all cases tubers are filled with stored food 

 material, mainly starch in the case of the potato. When 

 potatoes are set in the spring, the terminal bud grows 

 up to form the main stem of the new plant, while the 

 other eyes remain generally dormant. The new tubers are 

 formed from specialised underground branches produced 

 from the lower region of the main stem. The latter is 

 therefore often earthed up so as to promote the develop- 

 ment of these side shoots. It is a very common practice 

 before setting potatoes, to place them side by side with 

 the " rose " end uppermost and allow the terminal shoot 

 to commence its development in daylight. By this means 

 the shoot does not elongate so rapidly as when grown 

 underground, that is, in the dark, and thus the lateral 

 buds, which will develop into tuber producing shoots, are 

 more closely crowded together and more numerous. This 

 method therefore results in a greater yield of new tubers. 



