. The families of flowering plants. Plants; Phanerogams. 250 FAMILIES OF FLOWEEING PLANTS. of the plants are troublesome weeds. Thus the genus Hieracium or hawkweed, represented in this country by about 30 species, none of which are very troublesome, embraces no fewer than 250 species of the Old World; and of these the king-devil {H. praealtum) and the orange hawkweed (H. aurantiacum) have become serious pests to the farmers in many parts of New England and New York. In Maryland and the District of Columbia another European immigrant has become trouble- some, the gum succory {Ohondrilla juncea
. The families of flowering plants. Plants; Phanerogams. 250 FAMILIES OF FLOWEEING PLANTS. of the plants are troublesome weeds. Thus the genus Hieracium or hawkweed, represented in this country by about 30 species, none of which are very troublesome, embraces no fewer than 250 species of the Old World; and of these the king-devil {H. praealtum) and the orange hawkweed (H. aurantiacum) have become serious pests to the farmers in many parts of New England and New York. In Maryland and the District of Columbia another European immigrant has become trouble- some, the gum succory {Ohondrilla juncea). The ray flowers of the Chicory family are for the most part yellow, but the chicory itself has blue flowers, and there are other genera with white, pink and red rays. Family Ambrosiaceae. Eagweed Family. In this group the same floral structure prevails, except that the plants are monoecious or dioe- cious, and the pistillate head of flowers is frequently larger and nut-like or bur-like in appearance. The corolla is reduced to a mere ring or tube in the pistillate flowers; in the staminate it is tubular and 4-5- lobed; there is no flat or expanded portion corresponding to the rays of the Cichoriaceae. The ovary is inferior. There are 8 genera and about 55 species, largely American. The great bulk of them are pestilential weeds, of which the ragweed {Ambrosia artemisiaefoUa) may be taken as typical. (Fig. 220.) This plant, with its habit of overrunning every bit of waste land to the exclusion of all other plants, would be sufficiently dis- agreeable under any circumstances; but when we reflect that it is a dis- turbing factor, if not a primary cause, of the disease knows as hay fever, it must be accounted a vege- table pariah, to be combated and uprooted wherever it occurs. The cocklebur (Xantliium) is also trouble- some on account of the propensity of its prickly burs to adhere to every- thing with which they come in con- tact (Pig. 221). Family Compositae. Thistle or Composi
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