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COOK 



in Guatemala in 1904 showed characters often approached by- 

 seedling mutations, but somewhat more accentuated than any 

 of the similar mutations which have been raised from seedlings. 



Fasciation is, perhaps, to be looked upon as a form of bud 

 variation, but it must rise in some instances, at least, through a 

 derangement of the apical cells, rather than as a mutating adven- 

 titious bud. This has been observed very frequently in fascia- 

 tions of asexually propagated plants like Dioscorea and Ipomcea. 

 A normally round stem broadens gradually to several times its 

 normal width, but retains its original thickness or even becomes 

 thinner than before. 



Another instance in which heredity, in the usual sense of the 

 word, is suspended or set aside during vegetative growth, may 

 be found in the familiar phenomenon of galls, where the presence 

 of the insect parasite or the substances secreted by it, is able 

 to cause the formation of complicated and highly specialized 

 structures, as though new ingredients of heredity had been 

 added. 



The mutations which often occur in the first generation of 

 plants when grown in new regions are also to be reckoned as 

 post-reproductive changes of the hereditary type, for while we 

 could not be certain in any individual case, that the mutation 

 could not have occurred if the seed had not been transferred, 

 the very great difference in the percentage and the range of 

 mutations which can be secured from the same stock of seed 

 will prove that the new conditions have been an inducing cause, 

 able to act after the planting of the seed and long after the 

 nuclear elements have been arranged on a basis which would 

 normally have persisted throughout the life of the individual. 



The fourth type of interference with heredity during the 

 vegetative period is that of graft hybridism. The extent to 

 which this takes place with normal plants has not been ascer- 

 tained, but the power of communicating diseased conditions has 

 been well established in a variety of instances ranging from 

 peach -yellows, peach-rosette, and the mosaic disease of tobacco, 

 to the only slightly abnormal variegations. Mr. Luther Bur- 

 bank relates also an instance in which a graft of a red-foliaged 

 variety of Primus influenced the foliage and the progeny of 

 the stock. 



