on the Geography of Plants, 243 



zone only according to the proportion of the families of plants 

 in Lapland. In respect to the temperate zone, it cannot 

 clearly be shewn, how the author has produced the numbers 

 given for the same. As he had before exhibited the families in 

 Germany, France and North America, we could wish that the 

 numbers were the mean of the proportions of these countries ; 

 but as he gives in the superscription to the corresponding head 

 of the table a mean temperature of 10 — 14°, this cannot be the 

 case ; for to the northern part of Germany he ascribes a mean 

 temperature of only 8°. 5, to the southern part of France 16°. 7, 

 and in North America, according to him, the northern and 

 southern parts present a mean temperature of 18. (p. x.) It 

 were to be wished that the author had given the particulars of 

 his calculation here ; for no one can suppose that the numbers 

 were taken at hazard. In any case the proportion is not esti- 

 mated from all the plants of a temperate zone. 



But this method has two very obvious defects. The first is 

 this : the countries in question not being contiguous to each 

 other, we remain wholly uninformed, as to the proportions 

 of plants in the intermediate countries. I suspect that this 

 circumstance has occasioned the singular and contradictory 

 results in respect to the Ferns. In the treatise. No. 2, the author 

 says that the ferns as well as the Glumaceae, Amentacea?, and 

 some other families, increase from the poles toward the equator. 

 But as this conclusion stands in opposition to what has hitherto 

 been admitted in respect to the geographical distribution of these 

 plants, it is surprising that the author does not give in the table 

 the proportion of these families to the whole number of plants 

 found in the equatorial zone, and not only the proportion in 

 the temperate and frigid zones, which of itself is not sufficient 

 to verify his conclusion. In the treatise. No. 1. the ferns are 

 not placed by themselves, the number of which decreases frotn 

 the equator ; but the table is as in No. 2. He remarks, page 

 33, that the ferns in proportion to the whole number of phane- 

 rogamous plants decrease from Lapland to Germany ; but he 

 does not know whether they increase towards the equator, 

 because if the proportion be actually smaller in hot climates 

 than in Germany, for example as 1 : 50 in respect to the whole 



