the Pacific is that in the case of the Coni- cotyledons is that they include an unusual 



fers which belong to the southern hem- number of families which are entirely 



isphere, the continental masses which aquatic in their habit. These aquatic fam- 



pair in the display of similar forms are ilies are also world-wide in their distribu- 



Australia and South America. tion, so far as fresh and brackish waters 



Another fact, which is true of all large can be called world- wide. It is important to 

 groups, is that certain forms have a very notice that while the world-families which 

 extensive distribution, and others are belong to the land have worked out about 

 very much restricted in their occurrence, ten thousand different forms, the world- 

 For example, the greatest genus of Coni- families which belong to the water have 

 fers is the genus made up by the pines, at worked out considerably less than two- 

 least seventy kinds of which are recog- hundred different forms. This seems to 

 nized. This great genus sweeps through- indicate that the great number in the one 

 out all the north temperate regions of the case is due to the very diverse conditions 

 globe. There is a similar extensive dis- of the land, while the small number in the 

 tribution of the different kinds of spruce, latter case is due to the very uniform con- 

 larch, juniper, etc. On the other hand, ditions of water life. 



the giant redwood, known as Sequoia, is A third fact of importance is that the 



restricted to certain comparatively small Monocotyledons are mainly massed in 



areas in California. In China and Japan, the tropics, and in this sense are almost 



and also in Australia, there are numerous an exact contrast to the Conifers we have 



illustrations of forms very much restrict- been considering above. The same effect 



ed in their occurrence. of separation in working out diversity in 



The other great group of seed plants is structure is shown by the Monocotyle- 

 known as the Angiosperms, and to it be- dons as was shown by the eastern and 

 long all those seed plants which are most western Cycads, and the northern and 

 commonly met in this region. The dis- southern Conifers. For example, the 

 tribution of Angiosperms is a very much palms represent the great tree group of 

 more difficult question than that of Gym- Monocotyledons, and are restricted to 

 nosperms ; for while there are only about the tropics as rigidly as are the Cycads. 

 four hundred kinds of living Gymno- They are found in about equal numbers 

 sperms, there are more than one hundred in the eastern and western tropics, but 

 thousand kinds of living Angiosperms. there are no forms in common. The cast- 

 In presenting the distribution of this ern and western forms have become so 

 great group, it will be necessary to con- different that they might almost be re- 

 sider its two main divisions separately, garded as different families, 

 for they differ from one another very The Monocotyledons are also some- 

 much. One of the groups is known as what famous for the number of air plants 

 the Monocotyledons, to which belong which they contain that is, plants which 

 such forms as the grasses, lilies, palms, have sometimes been called "perchers," 

 orchids, etc. because they fasten themselves upon 



Some prominent facts in reference to trunks and branches and supports of 



the geographical distribution of these various kinds, and absorb what they need 



Monocotyledons are as follows : They directly from the air. It is a notable fact 



contain four great families, which include that these so-called "perchers" are very 



almost one-half of their number, and which much more abundant in the western trop- 



have become world-wide in their distribu- ics than in the eastern. An explanation 



tion. These families are the grasses, the for this is to be found in the fact that the 



sedges, the lilies, and the irises. This western tropics have a very much greater 



world-wide distribution means that these rainfall ; in fact, in the rainy woods of the 



families have succeeded in adapting them- Amazon region the air is saturated with 



selves to every condition of soil and cli- water, and everything is dripping, 



mate. In this world-distribution the One of the facts in connection with the 



grasses easily lead, not only among Mon- distribution of Monocotyledons is quite 



ocotyledons, but among all seed plants. puzzling, and that is the very poor repre- 



Another fact in reference to the Mono- sentation of the whole group in the south- 



43 



