352 
DIONAEA 
tive glands; unless stimulated, no secretion is carried on by them. 
On each half of the leaf are three long hairs — the trigger-hairs — jointed 
at the base so that they fold downwards when the leaf closes. The 
slightest touch given to one of these hairs, or a more vigorous stimulus 
applied to the surface of the leaf, causes an immediate closing of the 
two halves of the blade. The teeth cross one another, and if an insect 
cause the movement, it is thus captured. The closing of the leaf still 
continues till the two halves are tightly squeezed together. Then the 
digestive glands commence to secrete a ferment which acts upon the 
proteids of the prey and renders them soluble, when they are absorbed 
by the leaf (cf. Drosera and see p. 178). When the process is com- 
plete the leaf opens out again. [For further details, see Macfarlane 
in Contrib. from Bot . Lab. Pennsylv. Univ. I. 1892.] 
Dionysia Fenzl. Primulaceae (1). 12 sp. alpine Persia, Afghanistan. 
Dioon Lindl. Cycadaceae. 2 sp. Mexico. The seeds are ground into 
meal, which contains much starch. 
Dioscorea Plum, ex Linn. Dioscoreaceae. 150 sp. trop. andsub-trop. 
They have twining annual stems arising from tubers which in different 
sp. are of different morphological nature. In D. Batatas Dene. , &c. the 
tuber arises by a lateral hypertrophy of the hypocotyl, and is variously 
regarded as a rhizome or a root; in D. sinuata Vel., &c. it arises by 
lateral hypertrophy of the intemodes above the cotyledon; in D . 
peiitaphylla L., &c. it arises from the internode just above the coty- 
ledon together with the hypocotyl, whilst in D. villosa L., D. quin - 
queloba Thunb., &c., there is a fleshy rhizome. The tubers are known 
as yams; they contain much starch and are largely cultivated for food 
in tropical countries. They are propagated by cutting out the ‘eyes’ 
as in potatoes. Small axillary tubers often form cn the main stem 
and may also be used for propagation. 
Dioscoreaceae. Monocotyledons (Liliiflorae). 9 gen. with 170 sp. 
trop. and warm temp. Climbing herbs or shrubs with tubers or 
rhizomes at the base (the morphology of these is very varied ; see chief 
genera). Leaves alt., net-veined, often arrow-shaped. Infl. race- 
mose. Firs, regular, usually dioecious, inconspicuous. P (6), tubular 
at base; A 6, or 3 and 3 staminodes; G (3) usually 3-loc. with axile, 
rarely i-loc. with parietal, placentae. Ovules usually 2 in each loc., 
anatropous, one above the other. Capsule or berry. Embryo in 
horny endosperm. The tubers of Dioscorea are valuable as food 
stuffs; those of Testudinaria are also used. Chief genera: Dioscorea, 
Testudinaria, Tamus. Placed in Epigynae by Benth. -Hooker, in 
Liliiflorae by Warming. [See Queva, Rech. sur Panat. de Vapp. veget. 
d. Taccacees et d. Dioscorees, Lille. 1894.] 
Diosma Linn. Rutaceae (iv). n sp. S. Afr. Heath-like xerophytes. 
Diospyrinae (Warming). The 2nd cohort of Sympetalae (p. 137). 
Diospyros Linn. Ebenaceae. 180 sp: trop. Many sp. yield the 
valuable wood ebony. The sapwood is white and soft, the heart- 
