THE CARE OF SHADE TREES. 



139 



mists very quickly, 

 and their food materi- 

 tals are obtained from 

 the air and the mois- 

 ture which reaches the 

 plant. Mineral salts 

 are broug"ht to the 

 lichen by the dust in 

 the air, and probably 

 also by the dead bark 

 or the decaying" leaves 

 on the bark. Lichens 

 are really dual plants, 

 composed of fung-i and 

 alg'ae — the fungi hold- 

 ing the alg'ae as slaves 

 in the mesh-work of 

 the hyphae. The al- 

 gae, containing chlor- 

 ophyll, can make or- 

 ganic food out of the 

 inorganic materials at 

 their command, while 

 the fungus can feed 

 upon the organic food 

 thus prepared. (Fig. i 

 dent that the lichens 



Fig. 1773. A, Roestelia pirata on apple leaf ; (i) aecidia or cluster cups 



containing aecidiospores. B, Gymnosporangium macropus, (i) 



the cedar apple showing the yellow horns containing 



the teleutospores or winter spores. 



779). It is very evi- 

 which incrust the 



Fij?- '779- Lichens. 



bark of a tree do much harm in that 

 the breathing pores of bark are closed 

 and oxygen is unable to get access to the 

 interior cells. This loss of oxyg-en is of vital 

 importance to the healthy working of the 

 tree, and all shade and fruit trees should be 

 kept well cleaned. Careful scraping- will do 

 much good, but perhaps the best remedy is 

 the application of some strong caustic, such 

 as whale oil soap (2 lbs. to a g^allon of water 

 in winter) or fung-icide, as Bordeaux mixture. 



3. Fungi affecting the Leaves. 



(a) Maple Leaf Blotch [Rhyfisma aceri- 

 iiiim). (Fig^. 1780.) Frequently the upper 

 surfaces of the leaves of maples contain 

 larg-e black patches of a fung^ous nature. 

 , These patches make their appearance in 

 June, and are then yellowish in color, but a 

 little later they turn black and thick, forming- 

 a sort of scab, due to the fact that the my- 

 celium becomes hard and dense. During 



