FAMILIES OF FLOWERING PLANTS. 67 
disk or gland. The ovary is inferior, its tube united with that of the 
perianth, 3-angled, and often twisted, thus altering the natural position 
of the flower. These features are shown in figure 54. 
The family contains 410 genera and 5000 species, of wide distri- 
bution, but most abundant in the tropics. Probably no group of 
flowering plants yields a larger number of species valuable for green- 
house cultivation as ornamental plants. Representatives of nearly all 
the important genera may be found in every large orchid house. The 
most economic product of the family is vanilla, which is obtained from 
the fruit of the climber Vanilla planifolia and from several related 
species. The common putty-root (Aplectrum hyemale) of the eastern 
United States is said to furnish a valuable cement; while the substance 
known as sales is derived from the roots of the European species 
Orchis mascula. The genera which are important as yielding the 
most beautiful flowers in cultivation are Cypripedium, Cattleya, 
Laelia, Oncidium, Odontoglossum, and Lycaste. With the exception 
of the first, these are all exotics; but some of our native Cypripediums 
have flowers of great beauty. Figure 55 shows a cluster of the yel- 
low ladies’-slipper (C. Azcrsutum). Other native orchids of great 
beauty are Calypso, of the northern peat-bogs; Limodorum and Po- 
gonta, the grass-pinks; various species of /Zabenaria, with pink, pur- 
ple, orange or white flowers; and the delicate white ladies’ tresses 
(Gyrostachys). The reader is referred to various popular works for 
more extended descriptions of our native orchids, as it is impossible to 
admit extended details into this brief review of the plant families. 
For a full discussion of the peculiar modes of fertilization no work is 
more valuable than Darwin’s ‘Fertilization of-Orchids,’’ while several 
essays on this subject in the works of William Hamilton Gibson will 
be found most interesting. ? 
