PLANTS OP THE INDIAN DESEKT. 69 



placed. The stalk-cell is cylindrical. On the axis of C. microphyllus 

 there are large cells, bearing clothing hairs intercalated amongst 

 epidermal cells of ordinary dimensions. 



The glandular hairs are placed in epidermal depressions and 

 consist of an unicellular stalk-cell seated upon an epidermal cell which 

 is much depressed and of a head. The head is either club-shaped and 

 divided by horizontal walls as in. G. cretica (fig. 224) and G. glomeratus, 

 or spherical and divided both by horizontal and vertical walls as in 

 C. microphyllus (fig. 228), or flat and divided by horizontal walls as 

 in T. sindica (fig. 231) 



The lower cells of the head of club-shaped glands are also verti- 

 cally divided (fig. 224). The walls of external glands with spherical 

 heads are very thin. External glands seem to be absent in. B. 

 latifolia. 



Clothing hairs as well as external glands are less numerous on the 

 axis than on the leaf. This is due to the expanded surface of the 

 latter which is more exposed to direct rays of the sun. 



Structure of the Axis. — The epidermis consists of tabular cells with 

 outer and inner walls thickened and convexly arched outwards and 

 inwards respectively. The lateral walls undulated in C. cretica and 

 G. glomeratus. In G. microphyllus large pyramidal cells are inter- 

 calated amongst epidermal cells of ordinary dimensions and usually 

 bear clothing hairs. The cuticle is striated. The primary cortex is 

 characterised by the presence of assiruilatory tissue formed either of 

 palisade cells as in G. cretica (fig. 225) and C. microphyllus (fig. 229) 

 or of chlorenchyma as in other members (fig. 234). 



The pericycle in G. cretica and in both the species of Convolvulus 

 is composed of closely placed long thin groups of stone-cells ; in 

 I. sindica it forms a composite ring of stone-cells. In B. latifolia 

 the pericycle consists partly of isolated stone-cells and partly of very 

 small stone-cell groups. It undergoes reduction on a small portion 

 of the lower side of the inclined axis of C. cretica, where it consists 

 of a few isolated stone-cells. A well developed sclerenchymatous 

 pericycle is necessary on the upper side of the inclined axis to prevent 

 the axis from bending. 



The wood is composite. The vessels have simple perforations 

 and the medullary rays are uniseriate. The vessels are numerous and 

 are arranged in rows in G. cretica (fig. 225), C. glomeratus and I. 

 sindica (fig. 234) ; in other members the vessels are few. The abun- 

 dance of interfascicular wood prosenchyma is inversely proportional 

 to that of vessels. 



In both the species of Convolvulus and in /. sindica small portions 

 on diametrically opposite sides of the wood-ring are much narrowed 



1239—10 



