melts. For this to take place a reserve store of nourishment 

 is essential, and accordingly Alpine plants are furnished 

 with thick underground stems and fleshy roots where the 

 food substances can be stored. 



It is further interesting to note that the number of 

 plants that go through their life cycle in a single year and 

 then die off (annuals as they are called), is in the Alps 

 comparatively small, for most of the plants persist from year 

 to year. Kerner states that while only 44 per cent, of the 

 plants on the Danube plains are perennials, there are as 

 many as 96 per cent, in the Alps. That this has something 

 to do with the conditions under which the plants grow is 

 seen by the fact that the annual meadow-grass {Poa annua) 

 becomes perennial in the Alps. Annuals persist through 

 the winter season, only in the form of seed, so that a single 

 wet summer such as the last (1909), by interfering with the 

 ripening of the seeds, might threaten with extinction an 

 entire species. Annuals have but little food stored up for 

 a sudden outburst of activity on the approach of spring, nor 

 can the tiny root of a budding seedling obtain from the soil 

 all that is necessary for the rapid production of flowers and 

 seeds. Moreover, as we shall see immediately, the produc- 

 tion of seeds is in most plants very largely dependent on 

 the presence of insect visitors, and without them either less 

 fertile seeds or no seeds at all are in most cases formed. 

 Insects are said to be less numerous in the Alps than in the 

 plains, and thus the assumption of a perennial character 



xvi 



