382 PART IV. VEGETABLE TAXONOMY. 



Richardias and Calladiums belonging to the Arum family ; the 

 Lily of the Valley, Day Lilies, Tulips, Hyacinths, Tuberoses, 

 Tritomas and many others belonging to the Lily family ; the 

 Irises, Crocuses, and Gladioluses belonging to the Iris family ; 

 the Snowdrops, Daffodils, Jonquils and Amaryllis belonging to 

 the Amaryllis family ; and the Cypripediums, Oncidiums, Epi- 

 dendrums, Catasetums, Vandas and many other interesting plants 

 belonging to the Orchis family. 



CHAPTER XVI.— The Spermaphyta. 



THE ANGIOSPERM^; (Continued). 

 The Dicotyledons. 



The stems of Dicotyledons, like those of Gymnosperms, have 

 the collateral fibro-vascular bundles arranged radially about a 

 pith, and separated from each other by medullary rays, and in 

 nearly all cases secondary thickening takes place by means of a 

 cambium zone which lies between the wood and bark, but their 

 tissues are more complex, particularly those of the secondary 

 wood, which usually consist of wood-cells, wood parenchyma, 

 tracheids and ducts of various kinds, and frequently also of some 

 other tissues. The branching is always monopodial, and nearly 

 always from axillary buds. 



The primary root is often strongly developed, and with its 

 branches constitutes the principal root-system of the plant, but 

 adventitious roots are also common, and in some instances early 

 replace functionally the primary roots, as they do in Monocotyle- 

 dons. The roots in most cases undergo important secondary 

 changes, increasing in thickness by means of a cambium zone 

 and developing medullary rays resembling those of the stem. The 

 primary radial fibro-vascular bundle is usually few-rayed, and the 

 walls of the endodermal cells which enclose it are seldom thick- 

 ened. (See Vegetable Histology). 



The leaves are remarkable for the variety of their forms and 

 modifications ; they may be opposite, whorled or alternate, and 

 in many cases the phyllotaxy is quite complex ; they are fre- 



