SPECIAL CASES 603 



starch is deposited in the thirty years' old wood of the ash and oak, and 

 that the pith of Bctnla, Qiicrcus, Fraxinns, &c. may contain starch even 

 when twenty years old. 



A large portion of the nitrogenous reserves are apparently stored 

 up in the form of proteids, for in buds and young tissues more especially 

 proteids arc present which turn violet when treated with an alkaline solu- 

 tion of copper 1 . Amides are also of general occurrence, asparagin being 

 especially abundant in the roots of Robinia pscudacacia. 



Non-nitrogenous materials are preferably stored in the form of starch, 

 and this may frequently be partially or entirely replaced during winter 

 by sugar or fat. Fischer 2 has shown that in the oak, beech, and most 

 trees with hard wood, the main mass of the starch in the wood and medulla 

 remains unchanged during winter (starch-trees), whereas in the cortex the 

 starch may be entirely converted into soluble carbohydrates. In fat- 

 forming trees on the other hand the whole of the starch in the wood, 

 cortex, and pith is replaced by fatty oil, along with a little sugar. A rise 

 of temperature during winter or at the commencement of spring causes 

 the opposite change to occur, and this phenomenon may be repeated more 

 than once. Hence a secondary accumulation of starch is usually exhibited 

 in spring, and the amount present rapidly diminishes as growth is resumed 

 and consumption becomes active. In the meantime the young foliage 

 commences to assimilate and a maximum of starch is again reached in 

 autumn. The course of this periodic annual change is dependent upon 

 a variety of circumstances, and hence it differs much in different plants. 

 Th. Hartig 3 observed that the deposition of reserve starch began again 

 during the middle of May in the maple, in the larch in June, the oak in 

 July, and the pine in September. The starch is deposited first in the lower 

 parts of the stem and then higher and higher up, the deposition reaching the 

 young twigs of the maple at the beginning of August, those of the larch at 

 the beginning of October, of the oak in the middle of September, and the 

 pine in the middle of October. Fischer, however, has observed the recom- 

 mencement of the deposition of starch as early as May in certain cases. 



As is indicated by the power of bleeding and by the growth in 

 thickness, metabolism becomes active in spring before the buds have 

 opened, and as soon as this takes place large quantities of reserve-materials 

 are carried to the developing shoots, the starch in the stem disappearing 



1 Sachs, Flora, 1862, p. 331 ; Schroder, Jahrb. f. wiss. Bot., 1869-70, Bd. vir, p. 314. 



2 A. Fischer, Jahrb. f. wiss. Bot., 1891, Bd. xxn, p. 87. The literature is quoted here. Con- 

 firmatory observations by Mer, Compt. rend., 1891, T. CXII, p. 964 ; Siroz, Beihefte z. Bot. Centralbl., 

 1891, Bd. I, p. 342; Fiinfstiick, Beitr. z. wiss. Bot., 1895, Bd. I, p. 77. According to Rosenberg 

 (Bot. Centralbl., 1896, Bd. LXVI, p. 337), similar changes occur in rhizomes. 



3 Th. Hartig, Bot. Zeitung, 1858, p. 332. 



