THE MONOCOTYLEDONES 



1969 



containing one basal anatropous ovule. The former terminates in two or 

 three stigmas. 



The pollen grains are either spherical or oval and have a single delicate 

 coat. When the anther is ripe the flower stalk elongates, splits open the 

 spathe and the pollen grains are liberated. The pollen is of the same 

 densitv as water and pollination is said to occur below the surface. 



There is only a single genus Natas, which contains about thirty-five 

 species, many of which are widely distributed. Two species are now found 

 in Britain, but geological evidence points to the fact that the genus was once 

 more widely distributed and commoner in Britain than it is at the present 

 day. 



The Potamogetonaceae are a small family of about ten genera which 

 are generally submerged water plants, a few having floating leaves. Several 

 genera are found in sea-water. The stem usually consists of a rhizome 

 anchored by adventitious roots arising at the node. The leaves (Fig. 1896) 

 are produced alternately and consist generally of a broad, entire lamina 



Fig. 1896. 



-Potamogetoir natatis. 

 shoot. 



Flowering 



borne on a long petiole, or they may consist merely of a linear blade. Intra- 

 vaginal scales occur in the leaf axils. The flowers are either monoecious or 

 dioecious; the floral parts are either dimerous or tetramerous but a perianth 

 is generally absent. In many species the flowers are borne above water. 

 The anthers are sessile and the carpels free with solitary orthotropous or 

 campylotropous ovules. In Potamogeton the four anthers bear petaloid 

 outgrowths from the back of the connectives, simulating a perianth. The 



