523 



of the low temperature, no sufficiently strong growth of the inner side of 

 the perianth leaves takes place, so that the bending out of these leaves and, 

 therefore, blossoming is suppressed. The blossoms of Ornithogalum 

 umhellatum, Colchicum anfmnnalc, Adonis T'cryiaUs and others, react simi- 

 larly but more weakly. The processes in Mimosa pudica, Oxalis acetosella, 

 etc., prove that even green leaves act thermostatically because of the influ- 

 ence of lower temperatures. Material on this subject may also be found in 

 the later sections which treat of the mechanical effects of frost. 



The Rust Rings in Fruit. 



The so-called rust rings appear as the result of slight injuries from 

 frost in young fruits. By this are understood various formations of cork in 

 the skin of the fruit, spreading, especially in the pomaceous fruits, in ring- 

 like zones. In many varieties the appearance of cork-color etchings is a 

 very normal process. Our Reinettes, for example, often possess star-like, 

 small rusty spots. The so-called "netted Reinettes" have linear cork trac- 

 ings on the outer skin of the fruit and often such cork formations obtain 

 a surface-like extent, as, for example, in the French Reinettes, Parker's 

 gray pippin, in the gray autumn butter pear, the medlar, etc. This condi- 

 tion is morbid only when the phenomenon is very extensive in some years 

 (for example, 1900) on many fruit varieties which otherwise remain smooth 

 and when the formation of the cork covers the greater part of the fruit. 

 The initial stages are found in early youth. It is evident after the appear- 

 ance of very late May frosts that the contents of some groups of epidermal 

 cells turn brown and the cells begin to die. Beneath such places plate cork 

 is formed, and the dying epidermis becomes somewhat convex. During 

 the swelling of the young, green fruit, the formation of cork advances 

 further into the fruit flesh, producing considerable groups of parallel rows 

 of cells arranged perpendicular to the upper surface. In a special case 

 observed in "Amanli's butter pear" these cells, arranged in rows, appeared 

 to the same extent as those in the epidermal cells ; they were found actually 

 suberized, however, only in the peripheral layers while the light-colored, 

 thick walls of the more deeply lying cells gave a cellulose reaction. The 

 greater the new formation, the more the overlying, dying cell layers are 

 separated and the outer surface of the fruit becomes rough and scaly. 



In flask-shaped pears the pouchy part of the fruit, bearing the blossom 

 end, often appears to have rusty grayish scales, while the half toward the 

 stem is smooth and green. In other cases, a broad, cork-colored band is 

 seen near the blossom end, etc. At times with this splitting of the waxy 

 covering and dying of the epidermal cells is connected the development of 

 the newly produced underlying tissue into stone cells. These appear later in 

 circular aggregations on the outer surface of the fruit, so that the conditions 

 are produced which we have described as "Lithiasis" (p. 170). ("Diel's 

 butter pear," "Good Louise of Avranches"). Since such changes are usually 



