MULTIPLICATION IN PLANTS 



469 



by mice, rabbits, mechanical injury, some insect borer, or fungal 

 disease, they have had to be abandoned. There is no way by 

 which the removed bark with 

 its phloem vessels can be re- 

 placed after the destruction of 

 the cambium. By means of 

 bridge grafting, however, thou- 

 sands of trees are being saved 

 (see Fig. 192). 



343. Budding. In some one- 

 celled plants new cells are pro- 

 duced by means of outgrowths 

 or swellings, which have been 

 compared to "buds" on trees. 

 In the yeast plant (Fig. 178) 

 this can be easily seen. The 

 bud continues to absorb nour- 

 ishment from its surroundings 

 and to grow. It may put forth 

 buds on its own surface or it 

 may drop off and continue 

 growing and budding apart 

 from the mother cell. 



The buds on the twigs of 

 large plants are condensed 

 shoots ; each consists of stem 

 and leaves with modified 

 leaves or scales which serve as 

 protection. Single buds with 

 enough of the bark to include 

 the cambium may be removed 

 and grafted on a stock (Fig. 

 191). In propagating pota- 

 toes, pieces of the underground 



stem, or tuber, are used ; the new plants grow from the "eyes," 

 each of which is a complete bud, containing stem and leaves. 



Fig. 192. Bridge grafting 



Where the bark has been destroyed in a 

 complete ring around the trunk, the cam- 

 bium layer above the injury can be con- 

 nected with the cambium layer below 

 the injury by means of twigs that are 

 trimmed down to slip under the bark and 

 so bridge the gap. The growing layers 

 of the young twigs and of the old stem 

 grow together where they touch, and in 

 time the vessels, or ducts, furnish com- 

 plete communication between the roots 

 and the upper parts of the plant. By this 

 process many valuable orchard trees are 

 now saved for useful service 



