120 



FAMILIES OF FLOWERING PLANTS 



Everyone who lias penetrated a bog filled with sphagnum moss has 

 noticed the glistening reddish-lmed leaves of the round-leaved sundew 

 (Drosera rotundifolia), which is our commonest species. Its tiny white 

 flowers open singly, and the curved one-sided raceme elongates just 

 sufficiently to enable the flower of the day to point skyward, D.Jilifor- 



mis, with long slender leaves and rose- 

 purple flowers, common in the New 

 Jersey pine barrens and southward, 

 IS a more handsome plant (see Fig. 

 104). An examination of the leaves of 

 Drosera under a lens will show a mi- 

 nute drop of viscid fluid at the tip of 

 each hair; this serves to entangle small 

 flies, gnats, etc. In Dionaea, however, 

 the process of specialization has gone 

 even farther, and the leaf, which is 

 di%'ided at the midrib into two nearly 

 semicircular fringed lobes, closes like 

 a steel trap the moment any foreign 

 object comes in contact with the slen- 

 der sensitive hairs of its inner surface. 

 iy:'ter the imi)risoned object is thor- 

 oughly digested, the leaves again ex- 

 pand; if a bit of wood or other useless 

 material has been imprisoned, they 



Fig. 105. The coniinon river-weed (Podo- 

 stemon Ceratophyllnvi) . After Britton & Brown, 

 111. Fl. Northeast U. S. 



will open in a few hours. 



CHAPTER XXI. 



Order Rosales. 



This large and important order, of which the Rose family (Rosa- 

 ceae) is the type, contains seventeen other families, including the Pa- 

 pilionaceae, Mimosaceae, and Caesalpiniaceae, three groups which col- 

 lectively comprised the old order Leguminosae, and which include the 

 most valuable of our economic plants. In so large a group as the 

 Rosales, it is difiicult to find distinguishing characters which will apply 

 equally well to all the members; but in general the roseAvorts may be 

 known by the insertion of the stamens, which may be either hypoc/yjioufi 

 (on the axil below the pistil) or epi(jyuous (on the pistil itself); by the 

 sepals, which are more or less united or conduent with the receptacle; 

 and by the simple ovary, consisting of one or inanj^ distinct or united 

 carpels. 



Family Podostemaceae. River-weed Family. Contains about 21 

 genera and 175 species, all tropical except Podostemon, which is repre- 



