145 



Our two common jimson weeds {Datura Stramonium and 

 D. Tatula), barnyard weeds of probable South American origin, 

 have essentially the same habitat but usually occupy different 

 areas. They differ little except in color of stem and corolla, but 

 these differences seem to be constant, and they have been re- 

 garded as distinct by most authors ever since the time of Lin- 

 naeus. 6 



There are several other weeds that exhibit marked variations 

 not correlated with environment, but in form rather than in 

 color, and a few of those will be mentioned here, to call atten- 

 tion to the problem and stimulate further investigation. The 

 prickly lettuce, a weed not mentioned in our older manuals, and 

 probably of recent introduction, is now scattered over the upper 

 South and some additional territory, especially along railroads. 

 (It is not listed in Mohr's Plant Life of Alabama, 1901, but grows 

 now in Tuscaloosa, and various other places in the state.) It 

 has been variously called Lactuca virosa, L. Serriola, and L. 

 Scariola (these names all given by Linnaeus at different times). 

 The commoner form has leaves rather deeply pinnately lobed. 

 But another form, with leaves entire or nearly so (sometimes 

 distinguished as var. integrata), has exactly the same habitat 

 and perhaps a similar distribution, though the two are not al- 

 ways found together. In this case, asin Datura, we may possibly 

 have two distinct species introduced at different times, though 

 the difference is so trivial that one might expect hybrids or 

 intermediate forms. Such, however, do not seem to be on record. 

 Both have the leaves twisted into vertical planes, and they some- 

 times show a tendency to point north and south, as has been 

 observed before. 



In the vicinity of Tallahassee, Florida, and probably else- 

 where in that latitude, there are two species of pokeweed, 

 Phytolacca decandra L. and P. rigida Small, the former with 

 drooping racemes, and the latter with racemes erect or nearly 



other cases in the same genus, but I did not think it worth while to give it a 

 name. About 23 years later, S. F. Blake, quite oblivious of my contribution, 

 described the same thing from Appling County, Georgia, in a magazine which 

 circulates much less among students of southern plants (Rhodora 26: 231. 

 Feb. 1925), as forma Lowei, after the collector. 



6 This problem was discussed critically over 100 years ago by Dr. William 

 Tully, of Middletown, Conn. (Am. Jour. Sci. 6: 254-258. 1823.) 



