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POPULAR SCIENCE MONTHLY 



have been supposed to be without such hairs. Examination of speci- 

 mens taken from the lake bottom very carefully revealed their presence, 

 however, and aquarium cultures in the greenhouse show that, like those 

 on land plants, they are sensitive to the conditions of their environ- 

 ment. The presence of such hairs is almost prima facie evidence that 

 the organs bearing them have an absorptive function in addition to an 



anchoring one. This conclusion was tested 

 in several ways. It was found that such 

 plants could not make a normal growth un- 

 less rooted in favorable soil. Clean washed 

 sand could not be substituted for good rich 

 soil. Likewise a clay soil does not support 

 a normal growth. Thus we find that these 

 aquatics are quite sensitive to the nutritive 

 quality of the substratum. In fact their 

 existence depends upon this, as none of the 

 larger plants growing submerged in western 

 Lake Erie can mature a generation on the 

 nourishment they are able to secure from 

 the water alone. Chemical analysis shows 

 that plants which have been denied soil 

 nourishment are deficient in nitrogen, potash and phosphoric acid, as 

 compared with others allowed to root in the soil. 



Some plants are more dependent upon the soil than others, thus 

 Ranunculus aquatilis made .63 per cent, better growth in soil than in 

 clean washed sand. Elodea canadensis made 340 per cent, and Potamo- 

 geton perfoliatus 480 per cent, better growth in soil than in sand. 

 Such results show clearly how important a place the rooting aquatics 

 occupy in that chain of nutrient relations which stretches from the 

 fish down through the orders of animal and plant life to the soil. 



In the stocking of ponds for fish culture attention should be given 

 to the plants allowed to grow. The species mentioned above are favor- 

 able, while Ceratophyllum is not. The latter plant often makes a very 

 abundant growth. Though frequently accidentally anchored to the 

 bottom, it does not bear roots and must, of course, take its nourishment 

 from the water. A small lake in which this plant had made a very 

 abundant growth was found by another investigator to have less plank- 

 ton than other neighboring lakes in which the bulk of the vegetation 

 was rooting. 



Fig. a Villi isneriti spiralis af- 

 ter 5J4 weeks' grow th in clay soil. 



