THE FAMILIES OF FLOWERING PLANTS. 71 



mist a great part of the time. Ewart found coloring in abundance in 

 the vegetation on the summit of Pangerango (10,000 feet) in a very 

 dry atmosphere, and the writer has noted confirmatory facts in the 

 mountains of Arizona and New Mexico. 



The " screen " theory that the coloring matter is designed to pro- 

 tect the chlorophyll and plastic substances of the plant against intense 

 sunlight, is borne out by the above observations. The colors of 

 leaves serve other purposes as well, which the writer has discussed in 

 detail in a work now in press. 



University of Minnesota. 



THE FAMILIES OF FLOWERING PLANTS. 



By ( harlcs Louis Pollard. 



V. FROM PALM TO PINEAPPLE. 



IN order to approximate more closely the natural sequence of fam- 

 ilies this paper will be devoted to a number of small groups clus- 

 tering about the Liliaceae, and in the next issue of Plant World 



we will discuss the families announced in the last issue, complet- 

 ing the Monocotyledons. 



The Palms {Palmacecs) are so well known that the term " palm- 

 like," whether applied to a leaf or the trunk of a tree, is to most per- 

 sons self-explanatory. Equally, moreover, do we associate the palms 

 with the tropics, and with good reason, since the vast majority of the 

 140 genera and 1,000 species are confined to the warmer regions of 

 the globe. Of the few which reach our borders in the extreme south- 

 ern Atlantic states several are dwarf plants with prostrate or subter- 

 ranean trunks. The handsome genus Ncowashingtonia is native in 

 southern California. Whether native or exotic, a palm is always recog- 

 nizable from its peculiar leaves, and as the infioresence is not often 

 observed we may pass over the family without detailed explanation 

 of its characters. 



The Aroids {Araceoz) are a most interesting group, with great di- 

 versity of habit and structure. Most of the genera are tropical, but 

 our native forms are familiar to every student of nature. Who has 

 failed to welcome the skunk-cabbage as the earliest harbinger of spring, 

 albeit execrating the plant at the same time for its suggestively disa- 

 greeable odor? The curious hoods, scarcely peeping out of the ground, 

 are called spathes. They envelop the spadix, which is a fleshy spike 

 packed with small and inconspicuous flowers. This spadix, subtended 

 by the leafy spathe, is characteristic of the Araceae. The flowers 



