so 



25 



iiivestigated in variegated plaAts, in specimens in- 

 jured 'by parasites, etc.l Finally, cells which are consid- 

 erably smaller than normal ones may be grown in such a 

 way experimentally that an increase in cell volume is 

 mechanically prevented by putting the young parts of the 

 plant in plaster casts. If the nor^mal process of cell 

 division takes place at the same time, abnormally small 

 cells are produced.^ 



Abnormally narrow tracheal tubes are found not only in 

 the fibro-vascular bundles of dwarf specimens, but also 

 in poorly nourished individuals^, in etiolated plants, and 

 in individuals infected by fungi or arrested in their de- 

 velopment by gall-producing animals* 



IChe produ<5ts of the cambium also are variously ar- 

 rested in size, develop ; by diverse factors. Very 

 strong pressure may arreot the normal development of wood 

 cells. '^ In the same wgiy small-celled wood results 

 from disturbances in nutrition, Hartig has proved repeat- 

 edly in pines, that the tracheids are smaller in weakly 

 grovm speciiuens than in those normally developed. The 

 XvmeTL width of traeheal tubes in secondary xylem, especial- 

 ly is also easily changed by all possible injurious in- 

 fluences.^ Among others, Wiedersheim^ s interesting ex- 

 periments give much information as to the effect on growth 

 An- length of xylem elements. °. 



• 1. Timpe, Beitrag 2ur Kenntnis der Panachierung. Dis-"' 

 sertation Got ting en, 1900; Leist, Ueber den Einfluss des al- 

 pinen Standorts auf die Ausbildung d. Laubbl. Mitteil. 

 Jfaturf. Ges, Bern, 1889. Klebahn, Ueber eine Krankh. Vsr- 

 landeruaig d. Anemone nraiorosa etc. Ber. d« D. bot. Gesselsch. 

 1897, Bd. XV, p. 2&7. 



2. Compare the experiments of Hottes, Ueber den Emfl, 

 von Bruckwirtaingen auf di© Wurzel von Vicia Paba. Disserta- 

 tion Bonn, 1901. 



3. Compare for example, Pethrbridge, Beitr. z, Kenntn. 

 d. Einwirkung der anorganischen Salze auf die Bntwickelung 

 ^md. den Bau d. Pfl. Dissertation Gdttingen 1899; further 

 bibliogr^hioal references therein. 



4. Krabbe, Ueber d. Wachstum d, Verdi ckungsringes u.d. 

 ^ungen Holzzellen. Abhandl. Akad. Wiss,, Berlin 1884, 



p* 21. „ 



5. Bio Verschiedenheiten in der Qualitat und unanat. 

 Bau des Fichtenholzes. Forstl.- Naturwiss, Zeitschr., 1892, 

 Bd, 1, p. 209. V/achstumsunters. an Fichten, ibid, 1896, Bd. 

 V, p. 1. Further examples are described by H. v. Mohl 

 (Einigeanat. u, pUysiol. Bemerk. uber d, Holz der Baum- 

 wurzeln, Bot, Zei:^g. , 1862. Bd. XX, p, 269: Wiej^er, Ueber, 

 Bezieh. zw. d. sekund. Bickenwachstum u. d. Ernahrungs- 

 verhaltniss en der Baume. Tharander foa?stl. Jahrb, 1892, 



Bd. Xlill, p. 72; Holzbildung auf Kosten d. Reserve-materials 

 der Pflanzen, ibid. Bd. XLVII, p. 172. 



6. Ueber d, Einfl. d. Belastung auf die Ausbildung von 

 Hola, und Bastkoper bei Traurbaumen.Pringsheim's Jahrb. f. wiss 

 Bot., 1902, Bd, XXXVII, p 41. Compare also what is stated later 

 for "Rotholz" (Chapter V. A.) 



