790 



SCIENCE. 



[N. S. Vol. V. No. 125. 



our hypotheses would lead us to the infer- 

 ence that the larger groups would show 

 comparatively large quotas of weed species. 

 Is the inference true? 



Professor G. H. Perkins' Flora of Ver- 

 mont enumerates 114 families of Phseno- 

 gams and Pteridophytes in the State. Thus 

 if the species were equally divided among 

 all the families each family would in- 

 clude .87 per cent, of the total flora. The 

 great family of Composites, however, con- 

 tains 10.33 per cent, of all the species in 

 the State. Now, if it contained its fair 

 proportion of weeds it would have about the 

 same percentage. The fact is, it contains 

 21.43 per cent, of all the weeds and 33.33 

 per cent, of all the very bad weeds. This 

 family, at any rate, bears out the theory. 



These figures with some others appear in 

 the following table : 



SOME VERMONT WEED SPECIES. 



That is, these five great families include 

 nearly one-third the Vermont flora, but 

 nearly one-half the weed species and nearly 

 three-fourths the very bad weeds. 



Of coui'se, this does not demonstrate the 

 proposition and there are perplexing excep- 

 tions. Thus the largest family in the Ver- 

 mont flora, the Sedge family, contains not 

 a single species which could be reckoned 

 among the weeds. Nevertheless the fam- 

 ily is eminent both as to variability and po- 

 tential weediness. The sedges crowd out 

 pretty much everything else on their own 

 ground, and it is only because the agricultu- 

 rist seldom enters their favorite territory 



that their pernicious possibilities do not be- 

 come realities. 



Attention may also be directed to the 

 fact that many bad weeds have escaped 

 from cultivation. Since cultivation usually 

 induces variability, we may suspect that 

 this has been one source of aggressive power 

 in some weed species. 



Dr. Asa Gray * pointed out that both our 

 introduced and our native weeds are, to a 

 very great extent, cross-fertilized. This is 

 the more striking taken in connection with 

 the accompanying statement that most of 

 them are, nevertheless, capable of self- fecun- 

 dation. The latter capability protects them 

 from extinction when cross-pollination is 

 impossible, and the former provision gives 

 rise to effective variability when other 

 plants of proper relationship are near. 



Another surprising fact in the natural 

 history of our weeds is the very large pro- 

 portion of species introduced from Europe. 

 In a list of the twenty worst weeds of New 

 Jersey, prepared by vote, under the direc- 

 tion of Dr. Halsted, there were elected to 

 the twenty highest degrees of noxiousness 

 four natives and sixteen foreigners. I have 

 examined a similarly-prepared list of the 

 eighteen worst weeds of Vermont. This in- 

 cluded four indigenous species and fourteen 

 foreigners. 



Such a plain fact as this ought to have 

 some intelligible explanation. Dr. Gray, 

 in his paper mentioned, sets down a 

 common reason, namely, that, since the 

 greater part of the Eastern States was 

 originally tree-clad, the native species were 

 such as thrive under forest protection. 

 They are, therefore, unable to make their 

 wa}' in the cleared fields against immigrant 

 species which have been inured to such 

 conditions by centuries of thrifty practice 

 in the open fields of Europe. 



But a stranger fact of weed history exists 



*Am. Jour, Sc. and Arts, 3d Ser., XVIII. (1879), 

 161. Reprinted in ' Scientific Papers of Asa Gray. ' 



