52 THE BOOK OF NATURE STUDY 



found seeds of the Purple Loosestrife, the Water Cresses, Rushes, 

 Sea Milkwort, Sedges, Grasses, the Brook-weed (Samolus) in the 

 mud taken from birds. Cattle convey the seeds of marsh plants 

 through the mud which sticks to their hoofs. 



A large number of water plants, perhaps the greater pro- 

 portion, have their seeds dispersed by the wind. These plants 

 flower and seed well above the surface of the water, and their fruits 

 or seeds are provided with appendages which allow them to be 

 wafted about by the wind. Others are provided with hooks, 

 or bristles, which adhere to the rough coats of sheep, goats, oxen, 

 and horses that come down to the river, or marsh, and are thus 

 dispersed. 



Although most fruits and seeds are provided with structures 

 for dispersion, it is conceivable that they may not be carried any 

 distance from the parent plant ; but under certain circumstances, 

 such as the absence of wind or the non- visits of animals, may fall 

 in the immediate neighbourhood of the mother-plant. Nature 

 allows for great loss of seeds through many failing to germinate 

 for want of right conditions. When a plant sheds its seeds in its 

 own spot of ground the seeds on germinating must choke each 

 other, and only a few will grow into adult plants. The number 

 of seeds produced yearly by a single plant is enormous, and may 

 reach several thousands, but in order to keep up the present 

 number of plants, only a very few of these need grow up into 

 adult plants, and unless there were great loss of seeds the earth 

 would soon be too small to contain all the descendants of any one 

 plant. The loss of life, however, in seeds, in seedlings, and in adult 

 plants is immense, owing to changes of temperature, to floods, to 

 destruction by animals and by man ; and unless there were con- 

 trivances for dispersion, as well as an immense quantity of seed 

 produced, many plants would soon die out ; as it is, certain 

 water plants belonging to the Fen district are much rarer than 

 they used to be, owing to better drainage. 



THE COLOUR OF WATER INFLUENCED BY VEGETATION 



Many Algae give a distinct coloration to water, snow, and ice. 

 It is a matter of common experience that the rain-water in a cistern 



