REPORT OF THE BOTANIST. 85 



desired to grow other plants, Kentucky blue-grass, one of the most 

 valuable forage plants known, is quite difficult to subdue, owing 

 to its creeping root-stocks. On this account many farmers aim to 

 exclude it from their farms, jjref erring such plants as clover and tim- 

 othy, which, though inferior in some respects, are more easily sub- 

 dued. 



The following general hints on the destruction of weeds may be 

 found of use. Whether it be profitable to attempt the complete ex- 

 termination of weeds will depend on the price of land and labor, the 

 kind of crops to be grown, &c. There can be little doubt, however, 

 that the more troublesome perennial and biennial weeds can usually 

 be eradicated altogether with profit, especially where they are not 

 yet abundant: 



HINTS ON KILLING WEEDS. 



1. Plants cannot live indefinitely deprived of their leaves. Hence 

 preventing their appearance above the surface will kill them sooner 

 or later. 



2. Plants have greater need for their leaves, and can be more easily 

 killed in the growing season than when partially dormant. 



d. Cultivation in a dry time is most injurious to weeds and bene- 

 ficial to crops. 



4. Avoid the introduction of weeds in manure or litter or from 

 weedy surroundings. Some gardeners use no stable manure on 

 grounds they desire to keep especially clean, relying on commercial 

 fertilizers and the plowing under of green crops. 



5. After a summer crop has ripened, instead of allowing the land 

 to grow up to weeds it is often well to sow rye or some other crop to 

 cover the ground and keep them down. 



G. Give every part of the farm clean cultivation every few years 

 either with a hoed crop or, if necessary, with a fallow, 



7. It is often stated that cutting weeds while in flower will kill 

 them. This is only reliable with biennials, and with them only when 

 done so late that much of the seed will grow. 



8. If the ground is kept well occupied with other crops weeds will 

 give much less trouble. Keep meadows and roadsides well seeded 

 and i^low-land cultivated, except when shaded by crops. 



Cnicus arvensis (canada thistle). 



This thistle grows usually to the height of 2 or 3 feet, the stems 

 very leafy and much branched, with the flower-heads gathered into 

 small clusters at the end of the branches. The stem and branches are 

 not winged by decurrent leaves, as they are in many other species. The 

 leaves are comparatively small, those of the stem being mostly 3 to G 

 inches long, about half an inch wide in the main part, with three or four 

 prominent lobes on each side, and armed on the edges with an abund- 

 ance of sharp, rather stift\ prickles, which are 1 or 2 lines long. The 

 heads of the flowers are mostly less than an inch high, with a close in- 

 volucre, the small scales mostly without prickly points. The flower- 

 heads are mainly dioecious; that is, those of one plant are male only, 

 while those of other plants are female only. The plant has creeping 

 root-stocks, which spread deep beneath the surface and send up new 

 stems, thus multiplying the plant. Although this plant is called 

 Canada thistle, it is really a native of Europe, and has been intro- 



