134 



leaves (Crassula and mesembryanthemum types) etc. The most conspic- 

 uous example is the vegetation of the sea shore with its halophytic character. 

 Brick^ explains the fleshy and glassy constitution of the vegetative organs as 

 due to the abundance of sodium salts, which makes the parenchyma ex- 

 tremely turgid. 



The greater the number of examples showing the adaptation of the 

 plant to climatic conditions, the more marked will be the untt'na])ility of the 

 theory, that the cliniatic relations formed in each place of cultivation can be 

 changed at will without causing injury. If the whole sum of the climatic 

 factors should correspond in two widely separated localities this would be 

 no guarantee that the given plant would thrive as well in the new home 

 as in the old, since the distribution of light, heat and moisture can be proved 

 to be very different in the different periods of growth. The diseases of the 

 New Holland and Cape plants which, adapted to a dry climate, must pass 

 their lives in our sunless, damp conservatories, give the most abundant 

 proof. Decay of stem and root, dying of the twigs caused by Botr}'tis etc.. 

 constantly cause injuries to the successful cultivation of these plants. The 

 so-called damping off of the shoots of Pimelea, Chorizema, Pulteneae, Cor- 

 rea, Boronia, Agathosma, and Borosma, of Helichrysum, Humea etc., is a 

 result of the great humidity in our conservatories which can not be over- 

 come. 



5. Influence of Forests. 



The forestration of a locality modifies the influences of the position and 

 soil constitution and to this point pathology must pay especial attention. 

 The influence of forests is like that of surfaces of water, for, since organic 

 substances possess a higher specific warmth than do mineral substances, the 

 overgrown soil will be cooler, with an equal exposure to the sun, than the 

 naked rock or sand. The summer heat is also moderated by forests. With 

 the abundant evaporation of the foliage, the air becomes more moist, the 

 thicker the growth and the less motion in the air. Corresponding to the 

 greater evaporation, there is a more abundant cloud formation over forests 

 which is not so easily dispersed. Since the relative humidity of the air is 

 greater in and above the forest, much more dew is formed. The force of the 

 rain gusts is decreased. Since torrential rains, especially on slopes, cannot 

 be taken up as quickly, the mass of water runs off from the naked earth 

 and at the same time carries away the fine humus from the higher fields to 

 the lowlands. The annual repetition of this process so changes the conditions 

 of the fields that the higher places become impoverished and retain only a 

 slightly fertile soil skeleton, while on the low lands the humus layers keep on 

 growing. The power of the soil to retain water decreases with the loss of 

 humus and injuries due to a scarcity of water show themselves. In heavy 

 soils the steady beating of the rain drops in severe storms tends to form a 

 crust. 



1 Brick, Beitrage zur Biologie und verg-leichenden Anatomie der baltischen 

 Strandpflanzen. Cit. Bot. Jahresb. 1888, I, p. 765. 



