SYMPTOMS OF DISEASE (SYMPTOMATOLOGY) 



347 



trees of great age are formed by the action of the dimate of high 

 mountains, or by growth in porous sand on exposed sea dunes. Atro- 

 phy, or the non-formation of parts, or organs, is a phase of dwarfing. 

 It is seen in the dwindling of organs in size, as the result of various 

 causes, such as the attack of fungi. The carpels of Anemone are 

 atrophied in plants infested by Mcidium and the whole flower is sup- 

 pressed when the cherry is attacked by Ex- 

 oasciis cerasi. Exoascus pruni is responsible 

 for the absence of the stone in plum fruits, etc. 



6. Hypertrophy. — The undue excessive de- 

 velopment of a plant part is a symptom of a 

 diseased condition of that part. The bladder 

 plums formed in the plum pocket disease are 

 good illustrations of hypertrophied tissues, as 

 the replacement of the rye ovary by the ergot 

 sclerotium, following the entrance of the spores 

 of Clamceps purpurea. The attack of Gym- 

 nosporangium biseptatum (Fig. 136) results in 

 the massive enlargement of the stem of the 

 white cedar. A rust fungus is responsible for 

 the increase in size of the twigs and petioles of 

 our common ash and elder. 



7. Replacement: — ^A new structure takes 

 the place of organs. 



8. M ummifi cation. — The drying and 

 wrinkling of fruits and other plant parts 

 where the general shape of the part is pre- 

 served, but in a reduced size, is an evidence 

 of the unhealthy condition of that organ, or 

 part. The attack of the black-rot fungus, 

 Sphceropsis malorum, brings about a slow desiccation of the fruit which 

 may remain hanging on the tree over winter and in a shriveled condi- 

 tion. Frequently, the mummies produce a crop of spores, which spread 

 the disease. 



9. Alteration of Position. — The change of position of an organ from 

 its normal one'is a sure symptom of disease, usually the attack of some 

 fungous parasite. The normal position of the leaves of the house leek, 

 Sempervivum tectorum, is that of a rosette with the spirally arranged 



Fig. 136. — Swelling of 

 main stem of white cedar 

 caused by Gymnosporangium 

 biseptatum. (After Harsh- 

 berger, Proc. Acad. Nat. Set., 

 Phila., May, 1902.) 



