De ORCHID REVIEW. 
VoL. XVII.] JULY, 1900. [No. 199. 
THE EVOLUTION OF THE ORCHIDACE, 
(Continued from page 132.) 
THE essential characters of the great suborder Monandre were outlined in 
our last paper (p. 132), and we saw that they consisted of the reduction of the 
stamens to a single one in normal flowers, the cohesion of the pollen grains 
into pollinia, and the modification of the third stigmatic lobe into a 
rostellum, whose function is to secrete a viscous by which the pollinia are 
fixed to the body of the fertilising insect, these characters being adaptations 
to secure cross-fertilisation by particular insects. 
The rostellum is a new organ, and before going further it may be well 
to indicate its origin and function more clearly. It is a modification of the 
median or third stigmatic lobe, and the viscous it secretes is a modification of 
that of an ordinary stigma, but it possesses the property of drying very 
quickly on exposure to the air, while that of the stigma remains moist for a 
long period—a remarkable adaptation to secure its particular purpose. The 
rostellum is at first quite distinct from the anther, but in the higher genera 
the union of the two is so complete as to obscure the fact. The hybridist 
who touches the front of the anther of an Odontoglossum with a pencil or 
piece of stick in order to remove the pollinia for hybridising purposes, finds 
the yellow pollen masses attached to the apex of a slender white stalk, 
called the stipes, which proceeds from a small dark-coloured body, called the 
gland, but the two latter do not belong to the anther at all. They are 
portions of the rostellum, which only separate at a very late stage in the 
development of the flower, and adhere to the united mass of pollen grains 
from the anther cells which constitute the pollinia proper. This united 
mass, part male and part female in its origin, is called the pollinarium, and 
- is characteristic of the large tribe Vandez. 
The union of the pollen grains is another adaptation, all stages of which 
may be traced. In the higher groups the contents of each anther cell are 
covered by a waxy coat, while still earlier the pollinia are seen to be united 
into a number of little packets, each attached to a central axis by a little 
stalk, forming the so-called sectile pollinia of the Neottiee and Ophrydee. 
In the genera with powdery pollen the grains, if examined under a 
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