118 NATURAL HISTORY OF PLANTS. 



concretions of peculiar Ibrm and siliceous nature, which are not 

 attacked by any but fluorhydric acid. We will study them in 

 C. americana, which is rough on both surfaces. Above, this is 

 entirely due to the projection of these numerous projections seated 

 under the superficial layer of epidermis ; they are globular, of 

 unequal size, studded with minute tubercles like a cauliflower. 

 They may be compared to the cystoliths of Vrticacece and 

 certain Ei/pJtorbiacece ; they are probably less prominent in fresh 

 leaves. The inequalities of the lower surface are due to several 

 causes. First, the nerves project and form here a very rich net- 

 work, making it goffred as it were. Secondly, these nerves bear 

 two kinds of projections on their surface : stellate hairs, and con- 

 cretions like those of the upper surface, but smaller and more 

 distinctly tuberculate. The hairs consist of rays without septa, 

 tolerably acute and soft ; only at the base is there sometimes a 

 certain degree of rigidity. The concretions are very hard all over, 

 but often their lobes, more acute and projecting than usual, are less 

 rigid and more transparent, so that we find a sort of transition 

 between the superficial stellate hairs and the stony deposits of the 

 inferior epidermis. These concretions are found abundantly, though 

 of yet smaller size, in the areolae or meshes of the veins ; here, too, 

 the epidermis also presents a few small stomates. Here and there 

 are quite simple hairs. In certain Tetraceras these are very nume- 

 rous and quite simple ; in the leaves of Delima sarmentosa we find 

 some very flexible at the apex, but whose thickened base has 

 become hard through the deposition of the stony substance we so 

 often meet with in JJille/iiacea.'' 



Affinities. — We have seen' that Adanson first recognised the 

 complex affinities of the JJllle/iiacece with CistinecB, MagnoUacece, 

 and Ranunculacece ; it is beside the last two that most modern 

 botanists have agreed to place them. We have elsewhere stated' 

 that tlie DUleniacece represent BanunculacecB with the stem usually 

 woody, the calyx almost constantly persistent round the fruit, and 

 the seeds usually arillate. When the ovules are of Hmited number 

 and ascending in IMoiiacece, the micropyle is at first turned down- 



' Sec p. 113. - Hist, des Plantes, 70; Adansonia, iv. 36; vi. 273. 



