SPERMATOPHYTES 277 



earth's surface more completely than any other. The flowers are naked 

 and wind-pollinated, and the floral .numbers fluctuate widely. The 

 peculiarity of the group, which has suggested the name, is that the in- 

 dividual flowers are protected by bracts {glumes), the flower clusters be- 

 ing composed of these overlapping bracts. This method of protection is 

 in strong contrast with that of the preceding groups. 



The three preceding alliances are those which contain naked flowers, 

 and if this is a primitive character, these are the most primitive alliances 

 of the monocotyledons. It must be remembered, however, that this 

 condition may have arisen through reduction. 



4. Palmales (i family, iioo species). — These are the palms, the one 

 group including trees among the monocotyledons. The flowers have a 

 perianth, but it is not differentiated into calyx and corolla. In general 

 the floral numbers are indefinite, but there is occasional evidence of a 

 settling to three, especially in the carpels, which are not only usually 

 three in number, but also syncarpous. With the appearance of a 

 perianth, there is also the appearance of insect pollination, so that the 

 group as a whole is both wind-pollinated and insect-pollinated. It is 

 also characterized by the large sheathing bases of the leaves, which 

 invest the young flower clusters, a feature in common with the first two 

 groups. 



5. Synanthales (i family, 45 species). — This is a small and peculiar 

 South American alliance, which needs no description in this connection. 



6. Arales (2 families, 1025 species). — -These are the aroids, a very 

 distinct group of monocotyledons. The best known representatives 

 are probably Jack-in-the-pulpit (Arisaema) and calla lily, but numer- 

 ous tropical forms are in common cultivation in greenhouses. The 

 flowers are clustered on a fleshy axis (spadix), enveloping and often 

 overarching which is a great bract (spathe). The spathe is as variable 

 in form and variegated in color as are ordinary flowers, and associated 

 with it there is a development of insect pollination. In fact, the brightly 

 colored spathe seems to play the same part in aroids as does the corolla 

 in the higher groups. The flowers clustered on the spadix are exceed- 

 ingly variable as to the perianth; and although the stamens and carpels 

 are indeflnite in number, the number is small (1-4). A very distinct fea- 

 ture of aroids among monocotyledons is the production of broad, net- 

 veined, and frequently lobed leaves, which resemble those of dicotyle- 

 dons. One of the famiHes is made up of the duckweeds (Zflwrno), which 

 are very much reduced aquatic forms. 



