163 
While visiting thé estancia we drove across the country to 
the water-works of Santa Lucia, which supply Montevideo with 
water. The fields were gay with patches of scarlet, white, yel- 
low, blue and rose color, from the Verbenas, Anthemis, Senecios, 
dwarf Irids and Oxalids, which I had before collected at La Paz; 
and in places whitish patches of thistles extended for miles. I 
collected several species of thistles, but, as I had not brought a 
sufficient supply of paper with me, most of them were spoiled 
before I returned to Montevideo. I call them all thistles, although 
they are of different genera, since they are related to one another 
in structure and habit of growth, and are armed with spines. 
A large variegated thistle had just begun to bloom. It was 
the milk thistle, Sz/ydum marianum, Gertn., and is called by the 
natives ‘* Cardo asnal.” It has large purple heads of flowers, and 
leaves variegated with a network of white veins. It has been 
naturalized from Europe, and has also established itself on the 
Pacific coast of the United States. It is this species which Dar- 
win calls the “giant thistle of the Pampas,” Cynaria cardun- 
culus, also an introduced species, covered hundreds of acres. In 
speaking of the abundance of this and the preceding species in 
some parts of the Banda Oriental, Darwin says: ‘‘ There were 
immense beds of the thistle, as well as of the cardoon; the whole 
country, indeed, may be called one great bed. The two sorts 
grow separate, each plant in company with its own kind. The 
cardoon is as high as a horse’s back, but the Pampas thistle is 
often higher than the crown of the rider’s head. To leave the 
road for a yard is out of the question; and the road itself is 
partly, and in some cases entirely closed.” 
I noticed two other thistles, neither of which were indigen- 
ous—the star thistle, Centaurea calcitrapa, L., which has also 
“been sparingly introduced on the eastern coast of the United 
States, and the Centaurea lanatus, D.C. They were not yet in 
bloom, but the former species had its pretty pointed flower bracts 
well developed, forming symmetrical stars with spine-tipped rays. 
Of all the thistles, the cardoon was by far the most abundant. 
Darwin says that he doubts whether “ there is any case on record 
of the invasion on so grand a scale of one plant over the abo- 
