154 ME. C. DARWIN ON THREE SEXUAL FORMS 
With respect to Monachanthus viridis and Myanthus barbatus, 
these two forms are seen, in the specimen sent home by Sir R. 
Schomburgk, and preserved in spirits in the Society’s collection, 
to be borne on the same spike. They are represented in the 
diagrams, page 153. The flower of the Monachanthus, like that 
of the Catasetum, grows lower side uppermost. The labellum 
is not nearly so deep, especially on the sides, and its edges are 
erenated. The other petals and sepals are all reflexed, and are 
not so much spotted as in the Catasetum. The bract at the base 
of the ovarium is much larger. The whole column, especially the 
filament at its summit and the spike-like anther, is much shorter; 
and the front of the rostellum is much less protuberant. The 
antenne or horn-like prolongations of the rostellum are entirely 
absent. The pollen-masses are rudimentary : I could find no trace 
of a viscid disk or of a pedicel; if they exist, they must be quite 
rudimentary, for there is hardly any space for the imbedment of 
the disk. The absence of the antennz» in this Orchid, which has 
no pollen-masses to eject, is an interesting fact, as it accords with 
the view to which I have been led by an examination of three 
living species of Catasetum, namely, that the function of the an- 
tennæ is to convey the stimulus of a touch to the medial part of 
the rostellum, causing the membrane round the disk to rupture, 
and consequently the liberation and ejection of the pollen-masses. 
Instead of a large stigmatic chamber, there is a narrow transverse 
cleft close beneath the small anther. I was able to insert one of 
the pollen-masses of the male Catasetum into this cleft, which, 
from having been kept in spirits, was lined with coagulated beads 
of viscid matter and with utriculi. The utriculi, differently from 
those in Catasetum, were charged (after having been kept in spirits) 
with brown matter. The ovarium is much longer, thicker near 
the base, and more plainly furrowed than in Catasetum ; the ovule- 
bearing cords are also much longer, and the ovules more opake 
and pulpy, as in all common Orchids. I believe that I saw the 
opening at the partially inverted end of the testa with a large 
nucleus projecting; but as the specimens had been kept many 
years in spirits, and were somewhat altered, I dare not speak 
positively. From these several facts it is almost certain that 
Monachanthus is a female plant; and Sir R. Schomburgk saw it 
seeding abundantly.  Altogether this flower differs in a most 
remarkable manner from that of the male Catasetum tridentatum, 
and it is no wonder that they were formerly ranked as distinct 
genera. 
