CALYCIFLORiE 233 



characteristic of plants submerged in the water, where 

 the light is more diffused, and for this reason broad 

 leaves would be less advantageous to the plant in 

 its effort to catch the rays of the sun to carry out 

 the vital functions of carbon assimilation, etc. 

 Floating plants have broad leaves, the upper surface 

 being in this case fully exposed to the light and the 

 air. Therefore it is possible these half-submerged, 

 aquatic Horsetails and Mare's Tails have been origi- 

 nally submerged, and the Mare's Tail, in fact, has 

 entirely submerged leaves at an early stage. 



The Mare's Tail is found in most parts of the British 

 Isles, but is nowhere common, though perhaps more 

 abundant in Ireland than elsewhere. 



The habitat is shallow ponds, ditches, lake margins, 

 pools, etc. Mare's Tail sometimes grows at the 

 margin, sometimes in the middle, of a shallow lake. 

 I have seen it growing (as do Horsetails also) on dry 

 ground on the borders of a reservoir which has become 

 reduced in area and depth, competing well with such 

 plants as Pondweeds, likewise stranded on the dry 

 sloping banks, fifty yards from the water. 



This plant is found as a submerged or nearly sub- 

 merged plant also in the freshwater aquatic formation 

 in water relatively rich in mineral salts, but nearly 

 stagnant. It occurs in the broads of East Anglia in 

 the submerged leaf zone. 



It is of aquatic habit, with submerged leaves and 

 half-submerged stems. The rootstock is stout, 

 creeping, submerged. The stems are erect, simple, 



