THE EVOLUTION AND VARIATION OF FRUIT PLANTS. 23 



Degeneracy in the organs of fruit plants implies then nothing 

 pathologicall}^ or constitutionally injurious in character ; but means 

 only a step down from the genus, implying retrogressive or at 

 least arrested conditions. From a structural or anatomical view, 

 degeneracy is a loss of some elements without corresponding 

 development of other parts. Evolution has thus been not only 

 progressive but at times retrogressive ; its doctrine asserts an 

 endlessly irregular aJternation of epochs of life with epochs of 

 decay. 



Since living Nature gravitates towards progression and improve- 

 ment, it may justly be said that a fruit plant exists between the 

 two great tendencies of retrogression and advancement. While 

 progressive evolution develops the tree, extends the branch, 

 clothes it with verdure, expands the blossom, and ripens the fruit, 

 so degeneration lops the aged stems, prunes the weakly foliage, 

 trims the budding growths. And this degeneracy will often 

 depend upon external conditions of temperature, food, warmth, 

 and moisture, and may frequently be called spontaneous deterior- 

 ation when we do not know the cause of the phenomena ; that is, 

 a fruit plant may be advanced or degraded by the influence of 

 the physical conditions in which it lives ; for nature is always 

 willing to go backward or forward as the result of the law of 

 development. Each function of a fruit plant has its special limits 

 of temperature, which does not exist independent of that of the 

 exterior medium ; and when an equilibrium has been maintained, 

 the tree will grow ; but organized vegetable bodies are perpetually 

 mutable ; their growth is only slackened when the tissues become 

 mineralized. Each bud has its own existence, so long as it 

 attracts and elaborates the nutritive fluids ; and leaves often 

 terminate their foliaceous growth, decay, and fall off before the 

 appearance of autumnal cold. This change takes place only when 

 an excess of mineral substances encumbers the vegetable tissues, 

 and determines the death of the anatomical elements which they 

 contain. Extremes of heat and cold affect many of our fruit trees 

 and vines ; their anatomical functions soon cease when subjected 

 to a too elevated temperature ; while cold, which retards the 

 nutritive phenomena, will not always destroy but will merely sus- 

 pend them, because the vital activities and qualities are directly 

 derived from the physico-chemical properties in the midst of the 

 anatomical elements. Thus it is that fruit plants grow stronger, 

 languish, or hasten to final extinction, on account of the sway of 



