the Pacific is that in the case of the Coni- 

 fers which belong to the southern hem- 

 isphere, the continental masses which 

 pair in the display of similar forms are 

 Australia and South America. 



Another fact, which is true of all large 

 groups, is that certain forms have a very 

 extensive distribution, and others are 

 very much restricted in their occurrence. 

 For example, the greatest genus of Coni- 

 fers is the genus made up by the pines, at 

 least seventy kinds of which are recog- 

 nized. This great genus sweeps through- 

 out all the north temperate regions of the 

 globe. There is a similar extensive dis- 

 tribution of the different kinds of spruce, 

 larch, juniper, etc. On the other hand, 

 the giant redwood, known as Sequoia, is 

 restricted to certain comparatively small 

 areas in California. In China and Japan, 

 and also in Australia, there are numerous 

 illustrations of forms very much restrict- 

 ed in their occurrence. 



The other great group of seed plants is 

 known as the Angiosperms, and to it be- 

 long all those seed plants which are most 

 commonly met in this region. The dis- 

 tribution of Angiosperms is a very much 

 more difficult question than that of Gym- 

 nosperms ; for while there are only about 

 four hundred kinds of living Gymno- 

 sperms, there are more than one hundred 

 thousand kinds of living Angiosperms. 

 In presenting the distribution of this 

 great group, it will be necessary to con- 

 sider its two main divisions separately, 

 for they differ from one another very 

 much. One of the groups is known as 

 the Monocotyledons, to which belong 

 such forms as the grasses, lilies, palms, 

 orchids, etc. 



Some prominent facts in reference to 

 the geographical distribution of these 

 Monocotyledons are as follows : They 

 contain four great families, which include 

 almost one-half oftheirnumber, and which 

 have become world-wide in their distribu- 

 tion. These families are the grasses, the 

 sedges, the lilies, and the irises. This 

 world-wide distribution means that these 

 families have succeeded in adapting them- 

 selves to every condition of soil and cli- 

 mate. In this world-distribution the 

 grasses easily lead, not only among Mon- 

 ocotyledons, but among all seed plants. 



Another fact in reference to the Mono- 



cotyledons is that they include an unusual 

 number of families which are entirely 

 aquatic in their habit. These aquatic fam- 

 ilies are also world-wide in their distribu- 

 tion, so far as fresh and brackish waters 

 can be called world-wide. It is important to 

 notice that while the world-families which 

 belong to the land have worked out about 

 ten thousand different forms, the world- 

 families which belong to the water have 

 worked out considerably less than two 

 hundred different forms. This seems to 

 indicate that the great number in the one 

 case is due to the very diverse conditions 

 of the land, while the small number in the 

 latter case is due to the very uniform con- 

 ditions of water life. 



A third fact of importance is that the 

 Monocotyledons are mainly massed in 

 the tropics, and in this sense are almost 

 an exact contrast to the Conifers we have 

 been considering abowe. The same effect 

 of separation in working out diversity in 

 structure is shown by the Monocotyle- 

 dons as was shown by the eastern and 

 western Cycads, and the northern and 

 southern Conifers. For example, the 

 palms represent the great tree group of 

 Monocotyledons, and are restricted to 

 the tropics as rigidly as are the Cycads. 

 They are found in about equal numbers 

 in the eastern and western tropics, but 

 there are no forms in common. The east- 

 ern and western forms have become so 

 different that they might almost be re- 

 garded as different families. 



The Monocotyledons are also some- 

 what famous for the number of air plants 

 which they contain — that is, plants which 

 have sometimes been called "perchers," 

 because they fasten themselves upon 

 trunks and branches and supports of 

 various kinds, and absorb what they need 

 directly from the air. It is a notable fact 

 that these so-called "perchers" are very 

 much more abundant in the western trop- 

 ics than in the eastern. An explanation 

 for this is to be found in the fact that the 

 western tropics have a very much greater 

 rainfall ; in fact, in the rainy woods of the 

 Amazon region the air is saturated with 

 water, and everything is dripping. 



One of the facts in connection with the 

 distribution of Monocotyledons is quite 

 puzzling, and that is the very poor repre- 

 sentation of the whole group in the south- 



43 



