392 



KNOWLEDGE. 



OCTORER, 1910. 



are not only wideh" distributed, but in the cases 

 mentioned are real pests of farmers. In good garden 



soil, well culti- 

 vated for three 

 N'ears. we found 

 one thousand 

 and lift}- seed- 

 lings in a square 

 ^•ard on Ma\' 

 17th, 1909, and 

 of these seed- 

 lings six hund- 

 dred and tifty- 

 four were those 

 of creeping but- 



>•-#«. 



to weeds are very serious. The following examples 

 will suffice : — 



(1) The nitrogen in the dry matter of Persicaria 

 {Polygoniiiii Persicaria) was found to equal nearly 

 20 per cent, of albuminoids.* 



(21 A twenty-five-bushel crop of wheat was found 

 at the .\gricultural Experiment Station of Cornell 

 Universit\' to transpire (during growth) five hundred 

 tons of water. Weeds probabh- transpire to a some- 

 what similar extent. 



(3) Charlock (Sinapis arveiisis L.) and other 

 crucifers are hosts for the Turnip l~lea Beetle or 

 *■ Fly " (Phyllotrcta iieiiioriiin), the Turnip Gall 

 Weevil [Cciitorliyndius siilcicoUis), the Diamond- 

 Back Moth (Phitella luaciilipennis). I-~inger-and-toe 

 of Turnijis (PlasDWiiiopIiora hrassicae 

 Wor.), Peronospora parasitica De Bary, 

 and other pests. 



(4) Wolln\' has placed the annual loss 

 of crops due to weeds in Bavaria at an 

 a\'erage of JO per cent.+ Korsmo found 



Figure 2. 



Persicari.i or Kedsh.'uvk {Polygon iini 

 Persicaria L.) X I. This is a pest 

 of good arable land and gardens. It has 

 been quite destroyed by a 4 per cent, 

 solution of copper sulphate (100 gallons 

 per acre). 



tercup, one hundred and seven Poa 

 annua, and sixty were a species of 

 dock. Man\- seedlings were subsequently 

 destroved on the same square yard. 

 Plenty of other evidence as to the 

 prevalence of weeds could be adduced. 





The Harm Dune by Weeds. 



Many pages could be written dealing 

 with the losses caused b\- weeds, but 

 the matter can only be briefly mentioned here. 

 It mav be stated. howe\-er — and most readers of 

 Kxowledc;!-: will doubtless fully understand the 

 statements without further explanation — that weeds 

 take up the space which should be occupied by the 

 cultivated plant ; weeds rob the crop of food and 

 moisture, and of air. light and heat : they hinder 

 thorough cultivation, harbour injurious insects and 

 fungi, are parasitic on crops, may be j)oisonous, 

 stop up drains, and their seeds may very seriously 

 reduce the value of those of agricultural iilants. 



FlGl'RE 3. 



Pett\- Spurge {Eiipliorbia 

 Pcpins). n.atural size. This 

 weed is \ery common and 

 plentiful in some districts. 

 It appears to be protected 

 from spray fluids by a glau- 

 cous bloom on the leaves. 



the percentage 

 loss in money 

 V a 1 u e o n a 

 weedv com- 

 pared with a 

 clean plot of 

 barle\' to be 

 46 per cent., 

 and in the case 

 of potatoes 49 

 per cent.* E.x- 



FlGURK 4. 

 Corn Cockle iAgrosfciii ma Githago L.I 

 X H- Not only a weed in the usual 

 sense, but it is poisonous in a degree. 

 Spr.iying is partly effective and generalK- 

 prevents seeding (see text). 



..•hich hence require very thorough cleaning, involving perimental plots at University College Farm. Readings 

 considerable expense. " In short, the cash losses due showed that w ith two hoeings onh- after " smglmg " 



* Stutzer and Seidler. Fuhliiigs Laiidxc. Zcitung. June l.Mh. UlOS. p. 429. 



f Fr. Maier-Bode. Die Bekciiupfung der Acker-Vnkrduter. 



: Tidsskr. Xorske Laiuibr. 10 (1903.) 



