110 



MINUTE STEUCTURE OF THE KOOT. 



332. Sometimes there are papillar outgi-owths from these tra- 

 cheids, which are to be regarded as root-hairs. They occur 

 chieflj' on younger parts of the roots which are in contact with 

 a moist support, or which are kept wet. Thej- cling tenaciously 

 to moist surfaces, and may become much widened and flattened.-' 



333. The cortex of different plants varies greath' in thickness 

 and compactness, and in the thickness of the cell-walls. In 



a few cases remarkable lacunre are to be seen (e. g., Meny- 

 anthes) . 



334. The cells bounding the inner layer of the cortex have the 

 general characters described under " Endodermis ;" their radial 

 walls are generally more or less plicate, and there are no inter- 

 cellular spaces. 



335. In the primary cortex of roots all the various kinds 

 of secreting cells and receptacles for exudations described on 

 p. 97 may be looked for; but as a rule they are less developed 

 than in the stem. Collenclu'raa occurs sometimes in roots ; 

 e. (/., Raphidophora. 



336. The central cylinder has, at first, a peripheral lajer of 



1 Leitgeb : Die Luftwurzeln der Orchideen, Wien Akad. Denlischr., xxiv., 

 1865, p. 179. 



Fig. 90. Transverse section of tlie central cylinder of a root of a vascular cryptogmn 

 CMarattia Igevis): e, internal layer of tlie proper cortex; p, endodermis; m, peripheral 

 layer of I lie cylinder ; I, liber fascicles; ii, woody fascicles; c, conjunctive parenchyma 

 (pith and medullary rays). O'an Tlegliem .) 



