OF CATASETUM TRIDENTATUM. 155 
The pollen-masses offer so curious and good an illustration of a 
structure in a rudimentary condition, that they are worth descrip- 
tion; but first I must briefly describe the perfect pollen-masses 
of the male Catasetum. These consist of a large sheet of cemented 
or waxy pollen-grains, folded over so as to form a sae with an 
open slit along the lower surface ; into this slit cellular tissue enters 
whilst the pollen is in the course of development in the bud. 
Within the lower and produced end of each pollen-mass a layer of 
highly elastie tissue, forming the caudicle, is attached, the other 
end being attached to the strap-shaped pedicel of the pollinium. 
The exterior grains of pollen are more angular, have thicker walls, 
and are yellower than the interior grains. In the early bud the 
two pollen-masses are enveloped in two conjoined membranous 
sacs, which are soon penetrated by the two produced ends of the 
pollen-masses, and by their caudicles ; and then the ends of the 
caudicles adhere to the pedicel. Before. the flower expands, the 
membranous sacs including the pollen-masses open, and leave 
them resting naked on the back of the rostellum. 
In Monachanthus the two membranous sacs containing the ru- 
dimentary pollen-masses never open; they easily separate from 
each other and from the anther. The tissue of which they are 
formed is thick and pulpy. Like most rudimentary parts, they 
vary greatly in size and in form. The included, and therefore 
useless, pollen-masses are not one-tenth of the bulk of the pollen- 
masses of the male : they are flask-shaped, with the lower and pro- 
duced end greatly exaggerated, and almost penetrating through the 
exterior or membranous sac. The flask is closed, and there is no 
fissure along the lower surface. The exterior pollen-grains are 
square and have thicker walls than the interior grains, just as in the 
proper male pollen; and what is very curious, each cell has its 
nucleus. Now R. Brown* states that, in the early stages of the 
formation of the pollen-grains in ordinary Orchids, a minute areola 
or nucleus is often visible; so that the rudimentary pollen- -grains 
of the Monachanthus apparently have retained (as is so general 
with rudiments in the animal kingdom) an embryonie character. 
Lastly, at the base, within the flask of pollen, there is a little 
sheet of brown elastic tissue—that is, a vestige of a caudicle— 
Which runs far up the produced end of the flask, but does not (at 
least in somo of the specimens) come to the surface, and could 
not have been attached to any part of the rostellum. These 
rudimentary caudicles are, therefore, utterly useless. 
* Transactions of the Linnean Society, vol. xvi. p. 711. 
