1 21 



v©ry dry»-^ etc. The cork meri^tera also acts like the 

 carffbium. According to Douliot it is less active on the 

 shaded side of the branch than on that e:rposed to light. 



It is not surprising that the growth activity of the 

 cainhial ring not only loses its normal intensity by con- 

 tinued and sufficiently intensive action of the disturbing 

 factors , but also in places comes temporarily to a comple te 

 standstill . As a matter of course v;e do not need to re- 

 peat the fact that each 'process of grov/th presupposes a 

 minim-um of heat supply , nutrition, etc. We i/ill call at- 

 tention only to a fev/ cases in v/hich the interruption of 

 the normal processes of growth brings about variations in 

 the histology of i&e plants or of parts of them. Unfavor- 

 able conditions of light and nutrition retard in places 

 the setting of the cambial activity. ^ or can bring it to 

 a standstill for a number of years, or even |)ermanently. 

 Weak spruces discontinue their {;rov/th in thickness in the 

 lo^7er parts of the trunk; the brambles behave similarly. * 

 Mer (loc. cit.) observed on hyponastic conifer branches 

 that the normal grov/th in thickness progressed only in a 

 longitudinal half, and thus led to the formation of half 

 of an annual ring. How far "normal" life conditions and 

 fS6) "normal" phenomona of growth are involved in the produc- 

 tion of semi-annual rings is an open question, ^ 

 Finally, lerven factors Vv'ith a narrowly 



1, Oger, Etude, exper. de 1' action de I'humid, du 

 sol sur la struct, de la tige et d, feuilles, C. R. Acad. 

 Sc. Paris, 1892, T. OZV, p, 5E5. Further references on 

 reduced cambium activity are to be found in the treatises 

 quoted on page 26, ff, 



2, Douliot, Bech. sur la peridorme, Ann. Sc. Uat, 

 Bot, serie VII, T. X, 1889, p, 325; Infl. de la lum. sur 

 la devel. du leige. Journ. de Bot. 1889, T. Ill, p. 121. 



3, Hartig. Untersuchungen ub. die Entstehung u.d, 

 Eigenschaft des Eichenholzes, Forstl.-Iaturw, Zeitschr. 

 1884,- Bd. Ill, p. 1, Mer, sur les causes de variation de 

 la densite des bois, Bull.Soc. Bot, France, 1892, Tom. XXXIX 

 p. 95, etc. 



4, Hartig, Das Aussetzen der Jahresringe bei unter*- 

 druckten Stammen. Zeitschrift f, Forst - und Jagdwesen, 

 1889, Bd. I, p. 471. Ueber den Entwi eke lungs gang der Fichte 

 im geschlossenen Bestande nach Hohe , Form und Inhalt. Forstl 

 Sturw. Zeitschr. 1892, Bd. , I, p. 169, etc. 



5, Compare also Laramermayr, Beitrage z. Kenntniss 

 der Heterotrophie v. Holz. u. Rinde. Sitziingsber , Akad, 

 Wiss, Wein, math-naturw, Klasse, 1901, Bd. CX. 



