274^ 



GEOGItAPHY OF PLANTS. 



this family, the Stellatse, is almost peculiar to the temperate, 

 and especially to the northern temperate zone, while the 

 Spermacoceae and CofFeaceae are confined to the tropical zone. 

 The Cinchonese, indeed, grow chiefly between the tropics, 

 but always at a fixed height above the level of the sea, and 

 they also pass beyond the tropics. Plants with compound 

 flowers are indeed generally more abundant between the 

 tropics, but the group, which I have named Perdicieae (La- 

 biatiflorae, De Cand.), is peculiar to South America, and 

 descends even into the southern frigid zone. 



Respecting Ferns, it is understood that, in the temperate 

 7one, they constitute the sixtieth part of the whole vegetable 

 kingdom. But how little certainty attends such conclusions, 

 may be understood from this, that in New Zealand, the num- 

 ber of Ferns is to the number of other plants as 1 to 6 ; in 

 Norfolk Island, and Tristan d'Acunha, as 1 to 3 ; in Ota- 

 heite as 1 to 4 ; in Mascaren''s Island as 1 to 8 ; in Jamaica 

 as 1 to 10 ; in St Helena as 1 to 2 ; and in Egypt we have 

 as yet found but one species. The Grasses seem in all zones 

 to maintain nearly the same proportion : They constitute the 

 tenth or fifteenth part of the whole Flora. The Umbellatse 

 are evidently in greatest number in the temperate zone. 

 They constitute about the thirtieth part of other plants. To- 

 wards the pole they diminish in number ; and in the torrid 

 zone there are scarcely any other Umbellatae but some inter- 

 mediate forms, which only appear at a very considerable 

 height upon the mountains. The Cruciform plants exhibit a 

 similar proportion. In the temperate zone, they are to the 

 remaining plants perhaps as 1 to 20. Towards the pole they 

 decrease in number, and between the tropics we find scarcely 

 a trace of them. The reverse is the case with the Malvaceae. 

 Whilst these constitute, between the tropics, the fiftieth part 

 of the other plants ; in the temperate zone they bear to them 

 the proportion of 1 to 200, and in the polar zone they fail 

 entirely. The Leguminous plants are in greatest quantity 

 between the tropics, where they form the twelfth part of the 

 whole Flora. In the temperate regions they fail considerably, 

 and in the polar zone they are to the qther plants as 1 to 35. 



