YEW. 385 



plate but widening out into several layers outside the phloems ; (4) 

 the endodermis, with one or two layers of similarly thickened 

 cells outside it belonging to (5) the cortex parenchyma ; (6) the 

 piliferous layer, showing root-hairs in young root. 



In an older root the process of secondary thickening* is very 

 easy to follow ; the cambium arising on either side of the xylem 

 plate (which is still recognisable in the centre of quite old roots) 

 produces secondary xylem internally, and secondary phloem 

 externally, the primary phloem becoming crushed ; the cork 

 cambium arises from the outermost layer of the pericycle, producing 

 cork which cuts off all the outer tissues, the latter becoming 

 organised and thrown off. 



In a still older root, note the central primary xylem plate ; the 

 secondary wood showing annual rings ; the cambium ; the relatively 

 narrow secondary phloem ; the pericycle ; the cork. 



540. Male Flower. The Yew is dioecious ; pollina- 

 tion occurs in early spring (February or March), and the 

 seed ripens in the same year. 



Examine male flowers in early spring, and note (1) the 

 small size, globular form, and yellow colour of the flower ; 

 (2) its origin in the axil of a leaf, on the underside of a 

 twig produced in the previous season ; (3) the short stalk- 

 like lower part of the axis, bearing a number of brown 

 convex scales, which protected the male bud during 

 winter ; (4) the spirally arranged stamens, 6 to 15 in 

 number, on the upper part of the axis ; (5) the peltate or 

 umbrella-like form of the stamen, its pentagonal or 

 hexagonal disc-like head bearing about six pollen sacs 

 hanging around the stalk and fused together laterally. 



541. L. S. of Male Flower. In a longitudinal section of the 

 male flower, note (1) the axis, with its ring of vascular bundles ; 

 (2) the peltate stamens, each showing, if cut through the middle, 

 the stalk with a vascular bundle and the expanded head from which 

 arises on either side one of the pollen-sacs ; (3) the scales given off 

 from the lower portion of the axis. 



Note that the wall of each pollen-sac has a very distinct fibrous 

 or dehiscence layer, with the (J -shaped fibres on the cell-walls 

 better developed than in Pinus ; also that the pollen-grains have 

 no vesicles. 



When the male flower opens in spring, by the elongation of its 

 axis and the thrusting of the stamens beyond the scales, the 

 pollen-sacs on drying open in a curious manner the wall of each 

 sac splits at the base and along each side, and the outer portion of 



P.B. 25 



