862 



than 2 mm. (at least in the hornbeam) above the surface of the bark. After 

 a few years of such lethargy, the fibro-vascular body can renew its activity 

 and develop into a spherical, oval or even ellipical wood tuber. 



The death of dormant buds occurs of itself after a considerable number 

 of years, if not hastened by external circumstances, since the connection is 

 broken between the part of the bud lying in the bark and that in the wood 

 body by the interposition of the wood mantle of the branch which bears the 

 bud. The outer part of the bud, covered with scales and lying on top of 

 the bark, remains in place for some time; it dries up very slowly and finally 

 is thrown ofT. 



This bud, originally attached to the wood body, can also be loosened by 

 the splitting ofif of its fibro-vascular bundle from the wood of the trunk. As 

 a rule, the portions of the bud which project above the bark surface die, 

 while its fibro-vascular body, thus isolated in the bark continues to form new 

 wood layers and its own bark without the aid of foliage ; it must, therefore, 

 draw its plastic material from the surrounding green bark of the trunk. 

 This growth may continue for years ; the outer side of the wood tubers may 

 die from the destruction of external agents and, nevertheless, the tubers can 

 continue to form new wood on the inner side. In the red beech, as in the 

 hornbeam, these tubers are produced from adventitious buds. 



Th. Hartig^ describes the production of tubers in the red beech from 

 preventitious buds. The weak basal buds in the red beech die after possibly 

 twenty years inasmuch as the bud stem, lying in the bark, is separated from 

 the part of the bud in the wood by the interposition of a completely uniform, 

 connected wood layer of the branch bearing the bud. The part of the pre- 

 ventitious bud lying in the bark, however, can remain alive for some time 

 and leading, as it were, a parasitic life, grow by continued, concentric wood 

 formation, into those wood tubers which, as large as peas or hazelnuts, 

 project above the bark and are peculiar to the luxuriantly growing beech 

 trunk in middle age. 



Dutrochet-, whose personal view is related to the then prevailing bud 

 root theory, describes the tuberous outgrowths as bud embryos (meri- 

 thalles). Unlike the normal buds of the axis, these are not inserted on top 

 of and between each other but remain without any connection with the other 

 bud embr}'os and their vascular strands and, therefore, do not form a part 

 of the axial cylinder. So long as such an embryo, the primordium of an 

 adventitious bud, remains isolated in the other tissues, it develops no leaf and 

 no bud but retains its spherical form and grows by constantly developing 

 new wood layers, covered with their own bark. If this isolated wood body, 

 the primordium of an adventitious bud, finally comes in contact with the 

 axial body, its own bark disappears because of the pressure and the wood 



1 Hartigr, Th., VoUstandige Naturg-eschichte der forstlichen Kulturpflanzen 

 Deutschlands, p. 176. Berlin 1852. 



2 Observations sur la forme primitive des embrvons gemmalres des arbres 

 dicotyledon^s, 1837. (Nouv. M6m. du Mus. d'Hlst. nat. IV). 



