34 BUDS ON STEMS. 



rise in a special cellular tissue intercalated in the cortex, and on a branch in its first 

 year are not externally visible, because they are covered by the large hood-shaped 

 scale. The tissue of cells from which these small buds spring might be compared to 

 a callus if it were not produced on wholly uninjured branches and long before the 

 formation of cracks and fissures in the bark. In the second year, when the large 

 central bud begins to produce a lateral branch, throwing oflF the hood-scale and 

 elongating its axis, the small buds also become visible in the form of spherical or 

 oval knobs at the base of the new side-branch springing from the large bud. They 

 do not, however, get larger or smaller, but remain completely dormant and unaltered. 

 There is even a possibility of their never developing further, but in the event of the 

 branch at the base of which they were produced receiving an injury and dying, they 

 are aroused from their lethargy and grow out into leafy ramifications. It is obviously 

 their function to replace such of their predecessors as fall victims to unfavourable 

 external conditions. 



The Crack- Willows derive their name from the extraordinary fragility of their 

 branches. The hard bast and wood at the base of their one-year-old and two-year- 

 old branches exhibit a peculiar structure, the result of which is that a slight shock 

 is sufficient to sever the tissue, so that the branch breaks across at its base and drops 

 off. It seems to be an advantage for these Crack- Willows to get rid of certain leaf- 

 less and useless twigs which bear nothing but the scars of shed catkins, and are 

 merely an encumbrance. Thus much is certain, that several kinds of Crack- 

 WiUow cast off spontaneously a number of these branches, and that the buds above 

 described as lying dormant in the cortex put forth leafy shoots as substitutes. 

 Similar phenomena may be observed in Poplars. But in them the twigs break 

 off at a little distance from the base, and the substitution of green, leafy branches 

 for those covered with dead excrescences is effected by means of reserve-buds pre- 

 formed in the axils of former bud-scales. There can be no question of mutilation 

 in these cases any more than in the autumnal shedding of leaves which takes place 

 spontaneously for the benefit of the plants concerned, and is not susceptible to the 

 influence of external conditions except inasmuch as the latter may accelerate or 

 retard it. 



In all the cases hitherto described, the substitution-buds are developed in the 

 cortical tissue. At first, there is no direct connection between them and the woody 

 tissue of the stem; it is only when these buds are roused from their lethargy, and 

 called upon to put forth shoots, to replace anterior or collateral shoots which have 

 fallen, that communication with the wood, and to that extent also with the current 

 of crude sap, is set up by means of special conductive strands. 



There is, however, another form of accessory bud, which is connected from the 

 very beginning with the wood of the stem appertaining to it, and maintains this 

 during its whole life. In forestry the name of " dormant eye" already referred to 

 is employed in particular for this form of bud. If a year-old branch is examined, it 

 is found that the buds in the leaf-axils of its upper half are strikingly larger and 

 more vigorous than those near the base; indeed, above the point of insertion of the 



