132 Moore: The study of winter buds 



renew their growth in the spring varies considerably, as will be 

 seen from the following curves. The curve of Ulnnts americana 

 illustrates a retardation in growth of about two weeks beyond that 

 of Syringa vulgaris (figures A^ B). Querciis riibra and Quercus 

 alba vary somewhat (figures C^ D). The buds of the two species 

 oi Hicoria differ not so much in time as in rapidity of development 

 (figures E^ F), a greater delay in the swelling and unfolding of 

 the buds occurs in Ti/ia and in Bettda (figures G^ H). Buds of 

 the two evergreens, Rhododendron and Picea^ remain in a state of 

 apparent rest until a later date than the buds of any other species 

 that have been studied (figures /, /). 



Henslow (i 901) remarks : "Buds are primarily the result of 

 the lowering of temperature in autumn ; for as soon as this rises 



F 



above a certain degree they burst open and begin to grow." A 

 comparison of the curve of temperature with the curves of 

 growth indicates that temperature is not the only factor con- 

 trolHng the growth of buds. It will be seen that growth took 

 place in March at a lower temperature than in the preceding winter 

 months. Zero temperatures appear to have no effect on the size 

 of the bud. Buds both with dry and with somewhat succulent 

 scales were measured with the thermometer at o°F. No difference 

 in size could be detected as a result of these measurements. 

 Wiegand (1905) records a similar observation for buds but finds a 

 decided contraction in twigs due to the expulsion of air from the 

 intercellular spaces. 



As a rule, the first apparent evidence of growth in the bud is 

 in the appearance, at the distal end, of small tufts lighter in color 

 than the outer scales. These tufts were the elongating inner 

 scales, which were soon followed by the leaves themselves. The 

 increase in the diameter of the buds was proportionally much 

 slower than the increase in length. A comparison of the field 

 observations with the microscopic sections of the buds gives evi- 

 dence of growth within the bud before it becomes visible exter- 

 nally. This was most clearly apparent in Aesculns (figure 38). 



Such observations regarding the period of rest and growth in 

 buds may come to the eye of any careful and painstaking observer 

 in the field. What takes place within the scales during this time - 

 is not so easily observed, yet one must admit that the unfolding 



