1883. | Orchidee in the Natural System. 1247 
resent two of the largest branches of the great botanical tree. So 
that if we would find.the plants of the two classes which are most 
closely allied, it must be with the lowest forms of each, rather 
than with the lowest forms of the one and the highest forms of 
the other. Leaving now for the present the consideration of the 
Monocotyledons as lower in organization and structure, let us 
turn to the Dicotyledons and see what disposition can be made 
of the various orders, and which ones deserve to take the highest 
rank in the scale. 
The Polypetalæ, Gamopetalz and Apetale are the three classes 
into which the Dicotyledons have been generally divided, a divi- 
sion which, though in many ways artificial, is yet natural enough 
to serve our present purpose. Now there are several things 
which must be taken into consideration as establishing a high 
rank in the vegetable kingdom. Every one knows that the office 
for which every plant exists in nature, its chief function, is the 
production of seed, and the manner in which this is performed 
may be regarded as indicating, to a great degree, the relative rank 
of a plant in the scheme. This being granted, it can hardly be 
denied that those plants which produce the most seed with the 
least expenditure of material, and have at the same time the most 
perfect provisions for cross-fertilization, and are also among the 
most dominant families, should take a very high, if not the high- 
est rank in the system. 
Now of all plants in the world, the Composite take the lead in 
point of numbers and importance. Roughly estimated they 
number from ten to twelve thousand, and thus form about one- 
tenth of the whole number of flowering plants known. In some 
countries they constitute one-sixth of the whole flora, so that if a 
dominant type or family is a mark of high rank, where else than 
at the head should we place the Composite? That it should 
stand high would be immediately inferred from its very domi- 
hance. For if not of a highly specialized type it would never 
have been able to hold its own and increase to such an enormous 
€xtent, and occupy so large a space in the flora of the world. 
We recognize man as the highest type of mammal, and he too ts 
the most dominant and the most widespread. Another argument 
for the high rank of the Composite, is the fact that they have. 
been developed from the first most profusely in the tropics. 
There where the climate has been the most equable, most con- 
