2 BRITISH FLOWERING PLANTS OHAr. 



summer and winter temperatures, on the amount of 

 sunshine, of moisture, and various other factors. For 

 instance, some plants can stand a severe winter, pro- 

 vided the summers are sufficiently hot ; others are 

 satisfied with moderate warmth in summer, but cannot 

 stand a severe winter. Hence some plants will thrive 

 at Paris, but cannot maintain themselves in Kent ; 

 while others flourish near London, but are killed by the 

 colder winters of Paris. 



Apart from their systematic distribution in natural 

 orders, plants fall into certain great biological groups, 

 differing according to the point of view from which we 

 consider them. Thus they are annual, biennial, or 

 perennial, according as they run through their life- 

 history in one or two seasons, as do many of our herbs, 

 or persist for several or many years, as in the case of 

 some herbaceous plants like the Nettle, and all the larger 

 plants which become shrubs or trees. They may be 

 evergreen, retaining their leaves for more than one 

 season, so that the tree is never bare, as in Holly, Pines, 

 or Yew ; or deciduous, shedding at the end of each grow- 

 ing season the leaves which expanded earlier in the same 

 year. Again, while most live on land, many are aquatic. 

 In some the pollen is carried by the wind, in others by 

 animals, especially insects. 



Annuals and Perennials 



In very dry localities we find an unusual proportion 

 of annual species, which come up during the wet season, 

 if there be one, or after the rains which occasionally 

 occur. According to Boissier, annual species rise to their 

 maximum on the hot coast region of G-ranada, where, 

 out of 1070 species, 542 are annual, 46 biennial, and 

 482 perennial. 



Alpine and Arctic conditions, on the other hand, 

 favour perennial species. These generally have strono- 

 roots which go deep into the ground, and are thus pro- 

 tected from cold, while on the return of more genial 

 conditions they throw out aerial shoots. In the moister 



