260 THE ORCHID REVIEW. [SEPTEMBER, 1912. 
EVOLUTION OF THE ORCHIDACE. 
(Concluded from page 228). 
WE now come to the great subdivision of the Order in which the pollen 
grains have become agglutinated together into waxy masses, and in which 
the epiphytic habit is developed, the latter character, however, not 
universally, for many genera of both the Epidendreze and Vandez are 
terrestrial, hence the epiphytic habit was probably a later development. 
. The waxy condition of the pollinia may be regarded as a direct adaptation 
to prevent waste as Orchids became increasingly dependent upon insects 
for their fertilisation, and it probably arose quite independently of the 
sectile condition of the pollinia, which is another adaptation to secure the 
same end. In a few primitive types it is sometimes difficult to say where 
the powdery pollen ends and the waxy condition begins. The fundamental 
difference between the two is that in the latter the contents of each pollen 
sac remain cemented together in a waxy mass, and as the one apparently 
passed directly into the other we need not be surprised at the existence of 
a few types in which the character has not become fixed. Another 
evidence of a primitive state of development in Epidendrez is seen in the 
unspecialised rostellum, which performs the simple function of a secretory 
organ, producing a viscid substance for the purpose of gluing the pollinia to 
the body of the visiting insect. 
There appears to be almost a transition between the Arethusez and the 
Epidendrez, but we soon find a wide degree of diversity, both in structure 
and habit. One marked structural difference is that in the Epidendree 
the two anther-cells are often subdivided by longitudinal and transverse 
partitions, giving four and eight pollen masses, or occasionally—by an 
irregular development—six, instead of the original two, though they usually 
cohere together by the viscid secretion from the rostellum. Sometimes the 
pollinia are produced into caudicles at the base, as in many of the Leliez. 
Another marked structural innovation of the Epidendre is the development 
of a foot to the column, bearing the lip at its apex, a character often 
associated with an articulated or mobile lip, and evidently bearing a definite 
relation to the visits of the fertilising insect. The foot represents a further 
unilateral extension of the column, affecting the combined median petal and 
the stamens which unite with it to form the lip. This extension frequently 
affects the lateral sepals, which are then borne from the sides of the foot, 
forming a chin or sometimes a spur-like body, called the mentum, as in 
Dendrobium, or the lateral sepals may be carried up to the apex of the foot, 
as in Drymoda and Monomeria. Other structural developments that might 
be mentioned are the union of the sepals into a tube, as in Masdevallia and 
Cryptochilus, that of the lip with the column, as in Calanthe and 
