ORCHIDACEAE. 91 



A number of tropical epiphytic orchids have been brought in and are to be 

 seen in gardens fastened to or suspended from trees or grown in greenhouses 

 but they do not succeed very well, except under glass, though they flower at 

 intervals. Species of the large American genus Oncidium with yellow or 

 orange flowers in long wands or panicles are, perhaps, the most likely to suc- 

 ceed. Vanilla, a vine of this family, climbing by aerial roots, grown in tropical 

 regions for its pods, has been tried, but hitherto without economic success. 

 Among the genera grown in greenhouses mention may be made of Cattleya, 

 Dendrobium, Miltonia, Vanda and Selenipedilum. 



Sub-class 2. DICOTYLEDONES. 



Embryo of the seed with two cotyledons (in a few genera one 

 only), the first leaves of the germinating plantlet opposite. Stem 

 exogenous, of pith, wood and bark (endogenous in structure in 

 Nymphaeaceae), the wood in one or more layers surrounding the 

 pith, traversed by medullary rays and covered by the bark. Leaves 

 usually pinnately or palmately veined, the veinlets forming a net- 

 work. Parts of the flower rarely in 3 's or 6 's. 



Dicotyledonous plants are first definitely known in Cretaceous 

 time. They constitute between two-thirds and three-fourths of the 

 living angiospermous flora. 



Series I. Choripetalae. 



Petals separate and distict from each other, or wanting. 



The series is also known as Archichlamideae, and comprises 

 most of the families formerly grouped under Apetalae (without 

 petals) and Polypetalae (with separate petals). Exceptions to the 

 typical feature of separate petals are found in the Fabaceae, in 

 which the two lower petals are more or less united; in the 

 Fumariaceae, where the two inner petals or all four of them are 

 sometimes coherent; in some Crassulaceae ; the Polygalaceae, in 

 which the three petals are united with each other, and with the 

 stamens ; Oxalidaceae and Ilicaceae, whose five petals are sometimes 

 joined at the base. 



t Petals none (except in family Portulacaceae and in most Caryophyllaceae, 

 which are herbs with the leaves nearly always opposite, the seeds with endosperm, 

 and in the pistillate flowers of the walnuts, Juglans). 



Calyx none (except in the family Juglandaceae, trees with odd-pinnate leaves, and 



sometimes in Casuarinaceae). 

 Loosely jointed trees, the leaves reduced to verticillate scales. 



Order 1. CASUARINALES. 

 Plants not loosely jointed ; leaves normal. 



Herbs with small perfect flowers, in spikes. Order 2. PIPERAX.ES. 



Trees or shrubs ; staminate flowers, and some- 

 times also the pistillate, in aments. 

 Leaves simple. 



Fruit many-seeded ; seeds with a tuft of 



hairs at one end. Order 3. SALICALES. 



Fruit 1 -seeded. Order 4. MTRICALES 



Leaves odd-pinnate ; fruit a nut enclosed in 



a husk. Order 5. JUGLANDALES. 



Calyx present. 



Flowers, at least the staminate ones, in aments. Order 6. FAGALES. 



