374 CISTACE^E, OR ROCK-ROSE TRIBE. 



capsule, usually separating into five or ten valves ; along the 

 middle of each of which there is a placenta, or a partial dissepi- 

 ment. The seeds contain a small quantity of albumen ; and the 

 embryo is very curiously coiled up. All the species, in common 

 with those native to Britain, belong to the Linnaean class POLY- 

 ANDRIA, order Monogynia. 



537. This tribe evidently resembles the Poppies, in the tran- 

 sitory character of the flower, as also in the crumpling of the 

 petals ; but particularly in having a large number of hypogynous 

 stamens, and a seed-vessel partially divided, with numerous seeds 

 arising from parietal placentae. But, on the other hand, they 

 are separated by many points of difference ; for the calyx of 

 the Papaveraceae is formed of only two pieces which soon fall 

 off, whilst that of the Cistaceae is composed of five sepals, and is 

 persistent ; the former possesses a milky juice, which the latter 

 do not afford ; in the former, there is a large separate albumen, 

 whilst in the latter there is a small one. Further, they are 

 separated by a peculiar character which is of no small physiolo- 

 gical importance. The foramen of the seed, the aperture by 

 which the fertilising influence is received, and the radicle after- 

 wards makes its way out (. 436), is usually situated at the 

 'md nearest the placenta ; and the pollen-tubes pass into it, by 

 insinuating themselves along the cord which connects the ovule 

 to it. In the Cistaceae, however, the foramen is situated at the 

 point of the seed ; and the manner in which the pollen-tubes find 

 their way into it is very curious. When they have reached the 

 top of the ovarium, instead of passing down its sides to the pla- 

 centae, they separate themselves into bundles, of which one di- 

 rectly enters each cell of the seed-vessel, and spreads through it 

 like a fine cobweb, lengthening until it reaches the apertures of 

 the ovules. The plants of this tribe chiefly abound in the South 

 of Europe and the North of Africa, being scarcely known in 

 Asia and America. They are not known to possess any pecu- 

 liar properties ; a gum-resin termed Labdanum, which was once 

 used in medicine, is obtained from one species. They are all 

 low shrubs or herbaceous plants. 



538. The next tribe which will be noticed is also a small one, 



