396 Pub. Puget Sound Biol. Sta. Vol. 2, No. 56 



The fruits of the following plants did not sink within 30 days, the 

 duration of the experiment: 



Bidens elata Ranunculus pennsylvanicus 



Bidens cernua Rumex conglomeratus 



Epilobium panimlatum Rumex obtusifolius 



Typha latifolia Eleocharis obtusa 



Alnus oregona Polygomim hydropiperoides 



Aster eatoni Scirpus occidentalis 



Spiraea douglasii Roripa paulstris 



Hypochaeris radicata Sparganium androcladium 



Achillea millefolium Oenanthe sarmentosa 



Mentha piperita Holcus lanatus 



Rumex persicarioides Polygonium persicaria 



Erigeran canadensis 

 The fruits of Holcus lanatus germinated floating and continued to 

 grow on the surface until the end of the SO days. The hulled seeds of 

 Polyganium persicaria did not float so well ; only 60 per cent remained 

 afloat for 30 days. 



The fruits of the following did not all float for 30 days: Lactuca 

 pulchella, 10 per cent sank; Rumex occidentalis, 20 per cent sank; Plantago 

 major, all sank; Anaphalis margaritacea, 30 per cent sank and germinated 

 on bottom, 20 per cent germinated floating, 50 per cent floated without 

 germinating; Sisymbrium altissimum, all sank within 5 minutes; Juncus 

 bufonius, all sank at once. This last plant is a water loving one, growing 

 in wet places and close along fresh water shores, yet its seeds do not float 

 at all. 



No experiments were made to test the germinating power of seeds 

 which had been afloat for 30 days. Experiments designed to show whether 

 the seeds might lie in the mud on the bottom, and germinate when the 

 water recedes and uncovers them, were not conclusive; the indications are 

 that the seeds in the mud are not sufficiently abundant to explain the 

 distribution, although some are present. 



One other observation should receive attention. The seeds of Carduus 

 lanceolatus and Cardutis edulis, both common thistles in western Wash- 

 ington, may be distributed in a manner which seems not to be recorded. 

 They roll on quiet water like a tumbleweed on a prairie. The pappus is 

 not easily wetted and hence surface tension prevents sinking. Where 

 these plants are abundant one can find ponds whose margins appear from 

 a distance to have a line of froth. Examination proves it to be a ridge of 

 thistle seeds as much as 2 inches (5 cm.) high. The rate of rolling depends 

 upon the rate of the wind. The most rapid observed was about that of a 

 good walker perhaps 5 miles (about 8.1 km.) per hour. 



