863 



knot forms a real bud, which develops leaves. It now represents a gnarl 

 tuber (loupe) ; the coalescence of several such tubers forms a wen 

 (broussin). 



This theory differs from those developed earlier, inasmuch as in it the 

 bud is considered the final product of the tuber formation, while in the 

 others it is held to be the initial one. Lindley^ who describes the tubers 

 mentioned by Dutrochet in the beech, cedar and poplar and who found in 

 one poplar- that branches could develop from them, considers them to be 

 produced from adventitious buds and cites a further case in old olive trees, 

 mentioned by Manetti. He says that the tubers (gnaurs) in these trees 

 were cut out, together with a part of the bark, and planted and that these 

 tubers, which Manetti called Uovoli, gave young plants. Treviranus, to 

 whom Morren sent some cedar tubers, confirms in general the structure of 

 the tubers described by Dutrochet. He places in the same category the 

 phenomena of the isolated vascular bundles (leaf trace strands) in climbing 

 Sapindaceae, Calycanthus floridus and C. praecox, some Bignoniaceae, etc. 



Schacht'* explains the tubers in the bark of poplars, lindens, beeches, 

 etc., as dwarfed branches which have grown in circumference but not in 

 length. While Hartig points to the first beginnings of the tubers in dormant 

 buds, Ratzeburg* lays stress upon the bark as the productive centre of the 

 same beech tubers and says explicitly that they do not extend to the wood 

 body. Similarly Rossmassler' declares that the tubers of the mountain ash 

 (Sorbus aucuparia) , which he investigated, lie only in the bark and have no 

 connection with the wood body; Kotschy'', on the other hand, describes 

 bark tubers lo to 15 cm. large on the old trunks of the Lebanon cedar, as 

 gnarly, woody excrescences, firmly fixed in the bark, which are connected 

 with the mother trunk by a few vascular bundles. Masters^ also suspects 

 that some of the tubers (gnaurs or burrs) in the elm, etc., as also in many 

 apple varieties, are only aggregations of adventitious buds. 



A work by Krick** reconciles the apparently contradictory theories. He 

 has determined that the bark tubers (Sphaeroplasts) of the red beech de- 

 velop in connection with preventitious buds, either separating from the wood 

 axis of the trunk, or developing independently in the bark. In the latter 

 case the tubers have a woody, cork, or phloem core but never real pith. 



The latter kind of tuber formation which takes place in the bark paren- 

 chyma, outside of the primary group of phloem fibres, carries us over to the' 

 second group of bark tubers in which certainly no bud primordia participate. 



1 Lindley, Theory of Horticulture 198. Translated by Treviranus 1S50, p. 37. 

 - Loc. cit., p. 224. 



3 Schacht, Der Baum, 1853, p. 134. 



4 Ratzetaurg-, Die /Standortsgewachse und Unkrauter Deutschlands und der 

 Schweiz. Berlin 1859, p. 243, Note 1. 



5 Rossmassler, Versuch einer anatomischen Charakteristik des Holzkorpers 

 der deutschen Waldbaume. Tharandt. Jahrb. 1847, Vol. IV, p. 208. 



c Kotschy, Reise in den cilicischen Taurus. Gotha 1858, p. 267. 

 7 Masters, Veg-etable Teratolog-y 1869, p. 247. 



s Krick, Fr., tJber die RindenknoUen der Rotbuche. Bibliotheca botanica 1891, 

 Part 25; cit. Bot. Zeit. 1892, p. 401. 



