DIFFUSION OF SEEDS. 115 



5000 or 6000 eggs ; the smallest herring 100,000 ; the carp, of half 

 a pound weight, lays 362,000 ; the small perch 324,600 ; the sturgeon 

 7,653,200 ; and the codfish 9,344,000 ; yet the proportionate increase, 

 as we see, may not be greater than with higher animals or with plants 

 bearing a less number of seeds or eggs ; and the number would ap- 

 pear to be wisely adapted to the contingencies to which they are liable 

 and the probabilities of their failure to produce their kind. With 

 man there is a constant increase, as we notice, over the mortality, 

 though no such provisions are observed, while with the animals be- 

 fore mentioned it is doubtful if any increase is perceptible. 



Obstacles to the diffusion of plants are common. Some are found 

 no where beyond a certain spot, as the tree pink on the island of Crete, 

 and the double cocoa of the isle Praslin, though the nuts have been 

 widely diffused. The common thrift, the scurvey grasses, and the rose- 

 root are found only in rocky places, on shores or the tops of moun- 

 tains. Dry deserts, more than any other cause, intercept the diffusion 

 of seeds and plants. Districts of Africa, separated by burning sand, 

 exhibit widely different vegetation. Mountain ranges also present 

 extended barriers to the dispersion of plants, though their valleys, for 

 reasons before mentioned, are often enriched by various and valuable 

 plants. Plants on one side of a high mountain are very different from 

 those on the other side, as upon the Alps, and also on the Pyrenees. 

 On the eastern side of the Rocky mountains vegetation is not only 

 very different, when it is found on both sides, but there is little or none 

 for a great extent, on the east, while it is most luxuriant on the west. 



The natural orders of plants, are very important in their geographi- 

 cal distribution ; for this reason we notice a few primary divisions. 

 First, is the acotyledons having no cotyledons, or seminal parts surround- 

 ing and nourishing the embryo of the seeds. These include the mosses, 

 lichens, seaweeds, fungi, ferns, etc. ; 2d, monocotyledons, those with one 

 cotyledon, as the grasses, liliaceous plants, rushes, sedges, palms, etc. ; 

 3d, dicotyledons, those with two cotyledons, such as shrubs and trees, 

 and many herbaceous plants. Each of these have also other peculiar- 

 ities ; and in numerous instances, a peculiar station and definite geo- 

 graphical situation. Those of the 1st order increase as we proceed 

 from the equator towards the poles, the/er?w excepted, which most 

 abound in the tropics, in moist, hilly and sheltered places. The palms 

 of the 2d order are confined to the tropics, while the others of that 

 order vary ; some diminishing towards the equator and increasing to- 

 wards the north ; they mostly abound in the temperate zone, as with 

 the grasses. The 3d are most extensively diffused. The compound 

 plants of this order are an extensive family and are found on all parts 

 of the earth, but most abundantly in the torrid and temperate zones ; 

 yet they vary much in different situations of the former zone. In the 

 frozen zone the proportion of plants of this family is one half less 



