- absorption of moisture, and thereby promote the disengage- 
ment of the matter within. 
407. The pollen is said to be covered or protected by two 
membranes, but this point is still not satisfactorily determin- 
ed. 
408. Within each pollen grain, a peculiar slightly viscid 
fluid is contained, which constitutes the proper fecundating 
matter of the pollen, and has been called fovilla. 
409. When mature, the pollen grains open commonly by 
an irregular laceration of the integuments: Sometimes, how- 
ever, there is aregular dehiscence. On escaping into the stig- 
Matic tissue, but not till then, and always after the lapse of 
several hours, a peculiar tube— boyau, or intestine, as it is — 
called, is sent down, which constitutes a kind of channel or 
road for the transmission of the fovilla to the ovule. 
410. The presence of water seems to exert an ‘important 
action on the pollen, for it causes the rupture of the bags, 
the pollen mass will be discharged before it is ripe, and no 
fecundation of the ovary will ensue. Hence, a wet spring 
diminishes considerably the produce of the orchard. __ 
411. In aquatic plants there are various means to prevent 
the access of the water. In Zostera marina, a plant which 
grows in this country, the flowers are prueacted by an en- 
~velope, including a little air, while in many others, the plants 
elevate themselves to the surface when the pollen is ripe. 
This phenomenon may be observed in the Ruppia maritima, _ 
and several species of Potamogetons, common in this coun- 
iy, 
412. The number of stamens in different plants is very 
various. They are generally more numerous than the pistils. 
Flowers with one stamen are called monandrous ; with two 
diandrous, and so on. See the account of the Linnean 
System. 
THE POLLEN. 109 
and hence, if moisture be prematurely applied to the anther, _ z 
