Keegan The Hawthorn, 



145 



when a thicker-suberous tissue of flat cells is developed, which, 

 gradually becoming impermeable, leads on at an advanced age 

 to the production of a brown-red scaly and furrowed rhytidome. 

 The wood contains a little tannin and glucose, free phloroglucin, 

 and copious starch in summer, but in winter the latter becomes 

 reduced in quantity and appears confined exclusively to the pith, 

 medullary rays, and medullary sheath, whereas it completely 

 vanishes from the bark during the colder season. At the end of 

 May a branch inches diameter was examined ; the dried 



bark contained 1*25 per cent, of a yellow wax with, traces of 

 fat, but no carotin or terpene resin, also 7*1 per cent, tannin, 

 2 phlobaphene (free phloroglucin occcurs in the primary cortex, 

 bast parenchyma, and medullary rays), o*8 oxalate of calcium, 

 and 10 ash which had 4*6 per cent, soluble salts, 2 silica, 51*4 

 lime, 17 magnesia, and 1-23 P'-O" ; the wood yielded i per cent, 

 of ash which had 29*8 per cent, soluble salts, 32*8 lime, 8'5 

 magnesia, and 6 P-0\ The thorns or spines which stud the 

 smaller branches so obtrusively are not mere epidermal growths, 

 but, supported by vascular bundles, are really aborted organs, 

 due doubtless to the drainage and diversion away of food- 

 material for the support of flower and fruit ; according to 

 Lothelier dry air and strong light accelerate their production, 

 while humidity retards it and modifies their structure. 



Leaves. — The mesophyll is composed of two layers of pali- 

 sade cells about three times as long as broad and studded with 

 clear and sharply defined chlorophyll-granules, and also an 

 irregular lacunar tissue with large intercellular spaces; the 

 walls of the upper epidermal cells are straight, those of the 

 lower are sinuous, and both are free from hairs ; the stomata 

 are very large but sparse, their number being only about 131 

 per square millimetre of surface. The habitual deep division 

 of the lobes (especially in C. monogyjui) is connected with 

 a deficiency of nutritive material, which also ensures a very thin 

 tissue non-absorbent of heat. At the end of July the dried leaf 

 contains nearly 2 per cent, carotin and wax, with traces of resin, 

 but little or no fatty matter, 3*5 tannin and rutin, over 12 

 proteid substances, very little sugar, a very large quantity of 

 mucilage (formed mostly in the lower wall of the cells of the 

 upper epidermis), very much starch and oxalate of calcium, and. 

 6'9 ash which contains 19*7 per cent, soluble salts, i "6 silica, 

 38*9 lime, 4*7 magnesia, 4*3 P-O'', and 3*6 SO"'; there is very 

 little iron or manganese (distinguished from the Cherry) ; in the 

 autumn yellow and brown leaf the percentage of ash rises to 



1904 May I. K 



