August 14, 1914] 



SCIENCE 



241 



HETERODERA RADIOICOLA ATTACKING THE CANADA 

 THISTLE 



In addition to the large number of plants 

 known to be attacked by Heterodera radicicola, 

 the writer has recently had occasion to find it 

 infesting a new host — the roots of the Canada 

 thistle, Cirsium arvense. 



On December 10, 1913, the writer noticed 

 the first indications of the root knot, occur- 

 ring on tomato plants. This crop was being 

 grown in one of the greenhouses belonging to 

 the Department of Horticulture. On April 

 28, 1914, the plants were removed on account 

 of their unproductiveness. Many of the 

 plants, at the time of removal, showed their 

 entire root system infested and destroyed by 

 this eel-worm. 



On April 4, 1914, Mr. J. B. Poole, of the 

 department of botany, called the vsrriter's at- 

 tention to nodules occurring on the roots of 

 Cirsium arvense. These plants were growing 

 in a separate greenhouse from the one in 

 in which the tomato plants had been growing. 

 The knots were very numerous, varying in 

 diameter from two to ten mm. Their pres- 

 ence on the thistle roots, however, did not 

 seem to interfere with the growth of this weed 

 to any appreciable extent. A microscopic 

 examination showed that the roots were badly 

 infested with a nematode, and it seemed appar- 

 ently to be the same species which occurred on 

 the tomato. Cross sections of nodules showed 

 the egg-filled bodies of female nematodes 

 scattered throughout the cortex of the root. 

 Specimens were sent to the Bureau of Plant 

 Industry, and the determination verified. 



The soil used in the various greenhouses 

 was obtained from a nearby woodlot, and was 

 probably badly infested with Heterodera radi- 

 cicola at the time it was placed in the benches. 



The fact that this organism is capable of 

 living in the roots of Cirsium arvense should 

 warrant the necessity of placing additional 

 precautionary stress upon the eradication and 

 destruction of this weed. Care should be 

 exercised in treating soils before using, if the 

 above weed should occur in any of the central 

 or southern states, for the winters are prob- 



ably not severe enough to kill the eel-worm by 

 freezing. L. E. Melchers 



Depaetment of Botany, 

 Kansas State Agricultural College, 

 Manhattan, Kansas 



an avalanche of rocks 

 The Cadillac Trail on Mount Desert is one 

 of the most picturesque features of the island. 

 It is near Otter Creek and one enters the trail 

 from the shore road. The trail leads by a 

 gentle ascent to an irregular line of massive 

 rock fragments which have fallen from some 

 preexisting precipice farther up the mountain 

 side. The path runs through and under and 

 over these titanic blocks, some of which must 

 weigh hundreds if not thousands of tons. The 

 blocks and fragments stand at all angles. I 

 have had no opportunity to consult any book 

 on the geology of the island, but a hasty 

 examination of the region leads me to believe 

 that this avalanche of rocks must have fallen 

 from some precipice which had been undercut 

 by the waves when the land was below sea 

 level, as we know the whole New England 

 coast has been elevated since the ice sheet 

 retreated. The glacial clays with Arctic spe- 

 cies of MoUusks, still living in Hudson Bay, 

 are found from Danvers, Massachusetts, east 

 to Lubec, Maine, and beyond, and indicate 

 a former subsidence of the coast many feet 

 below the level of the sea. Now if this event 

 occurred at the time of this depression the 

 material buried beneath these rocks would be 

 of very great interest. If some large frag- 

 ment rested on the parent ledge it could be 

 tilted sufficiently by hydraulic jacks to enable 

 one to gather the stuff beneath, and it might 

 reveal the shells, diatoms, foraminifera, etc., 

 living at the time of this catastrophe, and pos- 

 sibly the compressed vegetation might reveal 

 important features also. The exploration 

 could be made at a moderate expense and the 

 conditions could be easily restored. 



Edward S. Morsk 



SCIENTIFIC BOOKS 

 ProUems of Genetics. By William Bateson. 

 Tale University Press. 1913. Pp. is + 

 255, illustrated. 



