104 THE JOURNAL OF INDIAN BOTANY. 



large clustered crystals in the neighbourhood of veins of all members 

 and in the cortex and pith of both species of Aerua and in A. aspera. 

 In the rhizomatous axis of A. tomentosa numerous clustered crystals 

 are present in the neighbourhood of water-storing tracheids, in many 

 of the medullary ray cells and in the pith. In the axis of P. lappacea 

 oxalate of lime is found in the form of crystal sand composed of 

 triangular granules in the cortex and pith. 



The veins are embedded except those of the mid-rib which are 

 vertically transcurrent above and below by collenchyma. They are 

 enclosed in bundle-sheaths of thick-walled green cubical cells in both 

 the species of Aerua. The mid-rib is furrowed above and prominent 

 below in A. pseudo-tomentosa, while in A. tomentosa it is prominent 

 above and below. 



The hairy covering (fig. 277) in the leaf and axis of both the 

 species of Aerua consists of a dense covering of candelabra hairs 

 which are more numerous on the lower surface. The underground 

 rhizomatous axis of A. tomentosa is quite glabrous. Clothing hairs in 

 A. aspera occur in the form of uniseriate trichomes composed of a 

 few basal cells and of a long terminal cell curved as on a hinge. 

 Walls are characterised by warts by means of which the hairs dove- 

 tail with one another and form a dense covering (fig. 282). Besides 

 clothing hairs, there are external glands composed of a uniseriate 

 stalk and of an ellipsoidal head (fig. 283). Uniseriate trichomes in 

 P. lappacea (fig. 279) are smooth-walled and consist of a basal portion 

 of a few short cells and of a terminal portion which is curved and is 

 composed of longer and jointed cells. The clothing hairs are filled 

 with air and become white ; they thus reflect light and glare and 

 arrest transpiration. 



Structure of the Axis. — The epidermis consists of small tabular 

 cells with outer and inner walls thickened and convexly arched out- 

 wards and inwards respectively. The primary cortex is characterised 

 by collenchyma at the angles and by an assimilatory tissue which is 

 composed of palisade cells in A. pseudo-tomentosa and of chlorenchyma 

 in other members. In the rhizomatous axis of A. tomentosa the 

 assimilatory tissue is not developed. The assimilatory tissue in 

 P. lappacea, forms a continuous ring, while in other members it 

 occurs between collenchyma groups at the angles. There is a layer 

 of green cells resembling the cells of the bundle-sheath, close below 

 the assimilatory tissue of both the species of Aerua. 



There is extensive development of cork in the rhizomatous axis- 

 of A. tomentosa. It extends between epidermis and pericycle and 

 also between the latter and the groups of soft bast. It is partly of 

 epidermal and partly of pericyclic origin. 



