HARDWICKE'S SCIENCE-GOSSIP. 



99 



more than a section of them, unless very slight and 

 almost theoretical injuries were taken into account. 

 For I suppose any wild plant growing where cultivated 

 plants are growing, or to be grown, must be regarded 

 as injurious to a certain extent, because it takes 

 nutriment from the soil ; but, if we had to define 

 exactly the extent of this injury, I think we should 

 often find it was hardly "visible to the naked eye." 

 There is another class of plants often called weeds, 

 which do not fall under either of the definitions given 

 above, namely, "poison-weeds," which grow wild 

 among wild plants, and are injurious to manor beast. 

 A case in point is the well-known "loco-weed" 

 (Oxtropis Lambcrti) of the Rocky Mountain region, 

 which has such dire effect on horses and other animals. 

 I do not think, however, that poisonous plants of this 

 kind have any real right to be classified with weeds 

 proper, and I shall omit them from the present slight 

 review. 



It has seemed to me that weeds might probably be 

 classified under two main heads : — 



1. Weeds which are not confined in any way to 

 cultivated land, and which do not disappear on land 

 that is highly cultivated, unless actually grubbed up 

 and removed. These weeds are aggressive, and 

 highly injurious to agriculture ; they usually belong 

 to large genera in large natural orders, and are 

 variable. 



2. Weeds which are mainly confined to waste or 

 cultivated ground, and which tend to disappear on 

 high cultivation, and do not commonly grow amongst 

 a heavy crop. These weeds are such as fail in com- 

 petition with other plants, and are not notably 

 injurious to agriculture. They probably often repre- 

 sent types nearing extinction, and commonly belong 

 to small genera or small natural orders, or both. 



Professor B. D. Halsted has suggested (inlitt.) the 

 terms aggressive and provisional to be applied to 

 these two classes. It is a singular thing to reflect that, 

 if all cultivated and waste ground were suddenly 

 covered with a coating of verdure, a large class of 

 plants would almost certainly become extinct from 

 sheer inability to cope with other plants in the struggle 

 for existence. Every one knows that when previously 

 verdant ground is broken up, and the earth, often 

 from quite a distance beneath the surface, is exposed 

 and bare, a crop of plants will often spring up which 

 did not exist before on the spot, and which will die 

 out again (leaving, no doubt, their dormant seeds) 

 when or if the grass and other sod-forming plants 

 assert themselves. 



Red poppies appearing on a continental battlefield 

 afford an historical instance of this. By almost any 

 roadside in England, the same thing is illustrated by 

 the little Urtica urens, asking only for leave to live 

 on some vacant spot. In Colorado, we have Cle'dme 

 integrifolia growing by roadsides, where hardly any- 

 thing else will grow, really usurping no man's land. 

 From its pods, it is often called " beanvveed." 



How different is the conduct of the thistles, which 

 belong to the "aggressive " division. It is no longer 

 " by your leave ; " with your leave or without it they 

 mean to grow where it suits them best, and if there 

 is a crop of something else so much the worse for 

 the crop. To look at a list of the North American 

 fauna, one might think the room for thistles was 

 already occupied. The Cnicus arvensis of Europe 

 thought differently, and, being introduced, has con- 

 trived to render itself unpleasantly conspicuous under 

 the name of " Canada thistle." Another composite 

 plant, which can hold its own in a rich English 

 meadow, has got imported into America ; this is the 

 ox-eye daisy {Chrysanthemum leucanthemicm), a pretty 

 flower, but none the less a weed, and an aggressive 

 one. It has even spread far westward, and is listed 

 among the twenty worst weeds of Kansas.* Arctium 

 lappa figures along with it, in the same list. 



It is luck for the English farmer that the climate is 

 not quite suited in the matter of warmth and dryness 

 for the common sunflower. Ifel/authzis annuus and 

 some allied species are terrible weeds in western 

 America. I have seen grain-crops so interspersed 

 with sunflowers as to often give rise to the sarcastic 

 remark, " So-and-so has quite'a little grain among his 

 sunflowers." This was in Custer and Fremont Coun- 

 ties, Colorado. Surely nothing but the climate has 

 prevented Hclianthus from running wild extensively 

 in England ; so there is some advantage, after all, in 

 what are not generally considered the beauties of our 

 English climate. 



Another imported weed of some note in America 

 is Chenopodiicm album. We have it in profusion 

 round houses in Colorado high up in the mountains ; 

 but it is not purely a nuisance, for, if your garden 

 crop fails, you are pretty sure to have a good crop of 

 " lamb's-quarter " in its place, which may be cooked 

 as spinach, and if picked at the proper time is equal 

 or superior to that vegetable. 



The purslane (Portulaca oleracea) is another noted 

 weed in America ; it figures in the twenty worst weeds 

 of Kansas, and (as Professor Halsted informs me) 

 also in the twenty worst weeds of Connecticut, showing 

 thus abundance at each end of an extensive range. 

 Professor Halsted points out to me that P. oleracea is 

 an exception to my classification of weeds, being a 

 great weed, and yet of a comparatively small genus 

 and natural order ; and, indeed, there are plenty of 

 exceptions of this kind, if searched for. Now it may 

 be that P. oleracea is classed thus highly as a weed 

 rather for its abundance than its aggressiveness, and, 

 after all, it is said to be good for feeding pigs ; but it 

 is rather more likely that it forms a genuine exception, 

 typical of a class of exceptions. 



Most weeds, as is well known, though existing 

 under circumstances of cultivation for ages, remain 



* Kellerman and Swingle, "First Annual Report, Kansas 

 Experiment Station," for 1888, p. 344. 



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