66 LEAVES. 



(37) Hemlock Leaves. 



The leaves of Conium maculatum, Linn. (N.O. Umbellifer?e). 



The epidermis is glabrous and bears stomata on both its surfaces, 

 but much more abundantly on the under than on the upper. The 

 cells of the upper epidermis are from 60 to 90/u long, and 30 to 45^ 

 wide ; they have somewhat wavy walls, whilst those of the under 

 epidermis, which are rather smaller, are sinuate and slightly 

 striated. Towards the extremities of the ultimate divisions of the 

 leaves the epidermal cells of the margin become papillose and bear 

 well-marked striations. The stomata are surrounded by four cells 

 which do not present any constancy in their arrangement. 



The mesophyll is heterogeneous and asymmetrical ; the cells 

 of the spongy parenchyma are stellate. 



The midrib is concave on the upper surface, and strongly convex 

 on the lower ; the epidermis of the latter is striated and covers a 

 layer of collenchyma. The meristele contains but little wood, and 

 there are no fibres in either the bast or pericycle. Immediately 

 below the endodermis, and opposite the centre of the crescent- 

 shaped bast, is a small secretory canal. 



There are no crystals of calcium oxalate, but the cells of the 

 upper epidermis contain sphsero-crystalline masses of unknown 

 nature which are soluble in caustic potash, but insoluble in 

 solution of chloral hydrate. 



The diagnostic characters of powdered hemlock leaves are :- 



(a) The papillose epidermis of margin ivith striated cuticle. 



(b) Absence of crystals of calcium oxalate. 



(c) Presence of sphcero-crystals in epidermis. 



(d) Absence of pericyclic fibres. 



