THE CONTINENTAL FLORA OF SOUTH SWEDEN 247 



to be found in the continental .si)ecics, and which may make the species depen- 

 dent on continental climatic conditions. 



The characteristics of a continental climate with regard to its importance to 

 plants arc above all scanty rainfall and cloudiness and within the temperate zone, 

 high summer temperature and low winter temperature, which has given rise to 

 marked vegetative and resting seasons. 



The scant}- (juantity of rainfall, or, rather, the scanty cjuantity of effective 

 rainfall, occasions that xerophilous character of the vegetation which is in the first 

 place distinctive of continental districts. The species are variously qualified for 

 Hfe with a scanty supply of water. 



There are available far too few detailed examinations of the connection between 

 the life functions of plants and the temperature of the vegetative season. In 

 certain species it has been established that their ecological »temperature optima* 

 (Schimper) form curxes rising from the germination to the ripening of the fruit 

 (e. g. Schimper, 1. c, p. 50). Hence the demands of plants for heat would be 

 at their greatest during the period of fruit-ripening. Each species has its special 

 optima for its different functions. As for continentally distributed species which, 

 in normal conditions, live under comparatively high temperatures during their 

 vegetative season, their optima may be supposed to be comparatively high up on 

 the scale of temperature. 



The low ?(>inter temperature involves a marked yearly resting season. Through 

 a great number of examinations it would seem to have been proved that such a 

 period is necessary for perennial plants of the temperate zone. During the season 

 of rest certain processes take place in the interior of the plant which form a 

 vital condition for it. The necessary length of the season of rest probably dep- 

 ends on hereditary qualities in the constitution of the plasma. It has been found 

 to be different in different species. This season of rest, caused by interior rea- 

 sons, is strongly influenced by exterior climatic conditions. Not till a certain 

 temperature is reached will the plasma be able to re-enter an active state, so that 

 the season of rest is generally much prolonged. Regarding the demands for a 

 minimum length of the season of rest with different species there are as yet too 

 few researches. It may perhaps not be impossible that with continental species 

 there are such demands in this respect as may be a contributive cause of their 

 absence in maritime districts. 



It has been found out that certain functions of plants have comparatively low 

 temperature optima. The development of genital parts and other organs ecologi- 

 cally combined with the latter, as the calix and the corolla, are promoted by a 

 comparatively low temperature (Jost, 1. c, p. 489). There is a great number 

 of observations of the fact that species removed to a spot, warmer at the time 

 of the formation of the flowers than tlieir native places, become more or less 



