362 NATURAL mSTORY OF PLANTS. 



anther, {U'liiscins: by two introrse or lateral clefts. In tlie bottom of 

 the receptacular sac we observe one or two carpels of Sangaisorha. 

 The fruits are aclienes, surrounded by the floral receptacle, whose 

 outer surface rarely remains smooth, being usually covered with 

 prickles, furnished at the tip with rigid, obliquely-reflexed hairs ; so 

 that eacli prickle is barbed like a little harpoon. In certain species 

 tlie prickles are unequal and scattered over the whole surface.' But 

 in a larger number they are as numerous as the sepals, arising from 

 tlie ujjper part of a rib continuous with the midrib of the sepal ; in 

 this case they are far better developed, and rise up more or less 

 oblicjuely outside the calyx." Acana comprises about thirty species 

 of herbs or undershrubs from the cold and temperate regions of 

 both hemispheres,'' chiefly the southern, inhabiting especially South 

 America^ and Oceania.' Their leaves are alternate, imparipinnate, 

 with two petiolary stipules. The flowers are in continuous or inter- 

 rupted heads or spikes, at the summit of a usually terminal axis, 

 naked below. 



Marfji/ricarpus^ (figs. 409, 410) has hermaphrodite flowers, with 

 the same elongated, narrow-mouthed receptacular sac. In the 

 bottom of it we find a single carpel, with one suspended ovule in 

 its ovary. On the rim of the opening, which is almost completely 

 closed up by the glandular layer lining the receptacle and only 

 leaving a narrow orifice for the style to pass through, are inserted 

 from three to five (usually four) imbricated sepals, but no calycle. 

 Interior to these are from one to three stamens, with slender 

 filaments and introrse two-celled anthers. The outer surface of the 

 receptacle bears four prominent vertical ridges, answering to the 

 midribs of the sepals. In one species of this genus, which has been 

 separated under the name Tetraglocliin^ each ridge later on becomes a 



' Tlie cristinctjvc cimractcr of the section Ch., i. 67, t. 103, 104. — H. B. K., Nov. Gen, 



Zuacana (DC.). et Sp., vi. 182.— C. Gat, Fl. Chil., ii. 282.— 



* This occurs in Anc'istrwm, made a distinct Wedd., Chlor. And., ii. 238, t. 76. 



gection by I)E Candolle ; hut we find every ^ Foest., Zoc. cit. — HooK, F., Fl. Antarct., 



transition between these localizid prickles, and p. ii. 9, t. xciv.-xcvi. — Benth., Fl. Austral., 



the scattered ones of Euaccena. These rigid recti- ii. 133. 



linear jtrickles are often covered with very stiff, ^ n & Vay., Prodr., vii. t. 33; Fl. Per. ef 



acute, rertexed hairs, altogether giving the Chil., i. 28, t. 8, tig. d. — Lamk., I>ict., Snppl., 



prickles the lofik of a niany-harhcd liarpoon. iii. 58'J.— DC, Prodr., ii. 591. — Endl., Gen., 



» WAi.r., lifp., ii. 43 ; v. 055 ; Ann., i. 280 ; n. 0378.— Spacu, Suit. « Bnffon, i. 485.— B. H.', 



ii. 519 ; iii. 855 ; iv. 664.— Vent., Ilort. CeU., Gen., 623, n. b'i.—Em2)etri spec. Lamk., Diet., 



t. 6.— LiXDL., Bol. Rffj., t. 1271. — Haev. & i. ry67.— And. ■it ri spec. Lamk., Ill , i. 77. 

 SoyiK,Fl. Cap.,\\. 290. ' V(Erp., Fragm. Synops., 26.— Endl., Gen., 



* Vahl., Fnum., 294.— R. & Pav., J'Z. Per.et n. 6376.— Wedd., Chlor. Andin., ii. 236, t. 77. 



