Cirsium COMPOSITAE 1001 



tically disappeared. Its disappearance was due to the butterflies Vanessa 

 cardui and Pyrameis cardui whose eggs are laid in the flowering heads, 

 the larvae eating the seed. This thistle is now infrequent to rare in the 

 state and I believe will be held in check by its natural enemy. In 1938 

 I have noted more specimens than for many years. 



Nat. of Eurasia; Newf. to Oreg., southw. to Fla., Nebr., and Calif. 



2. Cirsium Pitched (Torr.) T. & G. Pitcher THISTLE. Map 2195. 

 This species grows in almost pure, dry sand and is restricted to the dunes 

 near Lake Michigan in Lake and Porter Counties. It probably did occur 

 in La Porte County but I have not seen a specimen from this county. It 

 is commonest in the blow-outs. I planted seed in our garden, and when 

 the plants were three years old I measured the largest one. This plant had 

 a spread of 65 inches, and had 14 decumbent and radiating branches and 

 1 upright stem that was 28 inches high. The lateral branches had 110 

 heads, each branch with 5-10 heads. The upright stem had 14 heads. This 

 specimen had about ten times the number of heads that an average speci- 

 men has and was several times larger. 



Shores of Lakes Michigan, Huron, and Superior. 



3. Cirsium arvense (L.) Scop. Canada Thistle. Map 2196. This 

 species is infrequent to frequent in the lake area and is more or less local 

 south of this area. Since it is a very obnoxious weed, farmers have been 

 made acquainted with it, and they usually exterminate it as soon as 

 possible. There is a state law against harboring it, but the law is not en- 

 forced, and only occasional arrests are made. This species propagates by 

 underground stems and spreads rapidly. It is variable, and several varie- 

 ties have been described. I have not collected all of them, but three 

 varieties have been reported as established, and it is safe to assume that 

 they will persist until destroyed by force. Several bulletins have been 

 published describing the species and its varieties and give methods for 

 its eradication. One to be recommended is Bulletin 414 of the Ohio Agri- 

 cultural Experiment Station, by Freda Detmers, published in 1927. 



Nat. of Eu. ; Newf. and B. C, southw. to Va., Nebr., and Utah. 



3a. Cirsium arvense var. mIte Wimm. & Grab. This variety was re- 

 ported by Hansen (Proc. Indiana Acad. Sci. 34: 256. 1925) as established 

 in Blackford, Grant, and Henry Counties. 



3b. Cirsium arvense var. integrifolium Wimm. & Grab. This variety 

 was reported by Hansen (Proc. Indiana Acad. Sci. 35: 199. 1926) as 

 established in Grant and Hancock Counties. It is regarded by some author- 

 ities as a species, and, from its appearance and behavior, I believe it is of 

 specific rank. I know of a large colony in Wells County that was treated 

 with chemicals for two years and still it persisted. I have not visited the 

 colony recently. 



3c. Cirsium arvense var. vestitum Wimm. & Grab. This variety was 

 reported from Grant and Hancock Counties by Hansen. 



