CHAPTER XIII. 



DEPENDENT PLANTS. 



.Some plants, like animals, cannot make their own food, but 

 depend upon other plants for their food supply. 



Parasites and Saprophytes. — A plant which depends 

 upon another living plant is a parasite. Red rust is a para- 

 sitic plant which attacks corn-fields and gives the grain a sickly 

 yellow look. It may have been on the seed when it was sown 

 where the spores could attack the young plants as soon as they 

 germinated. 



When it fruits, short threads break through the surface of 

 the straw or leaves of the grain, and on their tips small spores 

 are borne. Spores formed in the early part of the season are 

 red. Later, black spores are formed. The spores make red 

 or black patches on the plant. When ripe they are blown by 

 the wind on to other plants, where they grow and send small 

 threads down into the grain again through the stomata. Since 

 they are taking the food, or some part of it, which the 

 grain-plant is making, the heads of grain do not fill out pro- 

 perly. For this reason, farmers try to get seed from grain 

 which is rust proof, for it has been found that certain varieties 

 of grain are resistant to the rust fungus, the fungus threads 

 (hyphaj) are checked after entering the stomata of the resistant 

 grains. This remarkable discovery is of great importance to 

 farmers (Biffen, 1905-7). 



Dodder (Ciisciita) and Cassytha are parasites which have 

 lost their leaves, roots, and most of their chlorophyll. At some 

 season of the year, however, Cassyt/ia stems are quite green. 

 Try to loosen the hold of these plants from the plants around 

 which they are twining and they betray their means of living, 



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