98 CLASS-BOOK OF BOTANY. 
diagram is reproduced here) came to the following con- 
clusions: Of the 6 staminal organs originally present, one 
(A:) of the outer whorl is represented by the fully-developed 
terminal anther of the flower, the other two (A, and As) of 
the same whorl combine with the lower petal to form the 
labellum. Of the inner staminal whorl, a and a, pass up 
the sides of the column, sometimes appearing as outgrowths 
or staminodia, as in ZLhelynutra, a common New Zealand 
genus of orchids, in which the flowers are nearly regular. 
(In Ladies’ Slipper — Cypripediwum—a genus not uncom- 
monly found in cultivation, A; is represented by a shield- 
like expansion on the top of the column, while a and a, 
form fully-developed stamens.) The third stamen of the 
inner whorl is quite undeveloped, the spiral vessel passing 
up the front of the column. Of the innermost whorl of three 
spiral vessels, two can be traced to the stigmatic faces, 
while the third, 7, ends in the rostellum. Although this view 
is only theoretical, yet it is so inherently probable, and affordy 
such an insight into the modifications which take place in the 
development of floral organs for definite purposes, that it is 
well worth studying. We should judge from it that the pro- 
genitors of all orchids had regular flowers with perfectly 
trimerous symmetry, but that their mode of fertilisation 
became more and more specialised, until at last they became 
dependent on certain kinds of insects to perform this necessary 
work for them. In course of time species of some genera, 
such as Dhelymitra, Microtis, and Prasophyllum, appear to 
have retrograded in development so far as to become self- 
fertile once more; but the majority of orchid-flowers are quite 
Fig. 195. Column Fig. 196. Column 
of Thelynmtra, of Thelymitra, 
side view front view 
Fig. 194. Flower of Thelymitra (mag.). (mag.). 
pulchella, front view. 
incapable of self-fertilisation. In the first-named genus the 
flowers tend to revert to regularity of form as far as the 
perianth is concerned, but in other respects retain the typical 
orchid-structure. 
