BUDS ON STEMS. 31 



are only subsequently foi-med in the cortex in the immediate neighbourhood of the 

 points of origin of shoots which have already withered. The latter is of com- 

 paratively rare occurrence. In Spartium, scopariuin, which is represented in vol. 

 i. p. 331, one bud only is produced in each axil. The following year, this bud grows 

 out into a long switch, and at the same time a new bud is initiated in the cortical 

 tissue just beneath the base of this shoot. If the first shoot dies next yeai-, as often 

 happens, especially in the case of plants growing near the northern limit of the 

 Mediterranean region, the second bud produces a shoot, and close under its base is 

 formed once more the rudiment of a bud for future substitution. This may go on 

 for several years until at last a whole row of withered stumps are to be seen above 

 the last substituted shoot. This mode of growth, which has been observed not 

 only in Spartium, but also in several allied PapilionaceEe belonging to the Mediter- 

 ranean Flora, is very prejudicial to the freshness and vigour of the plant's appear- 

 ance. The presence of a number of withered remnants crowded together produces 

 an impression of disease and starvation; else, as an alternative, one is tempted to 

 suppose that the bushes have been cropped by cattle, or annually truncated by 

 man, whereas they themselves accomplish all these changes without any damage 

 of the kind being inflicted. 



In Robinia Pseudacacia, the plant known by the name of Acacia, a single bud 

 is formed at first in the axil of each foliage-leaf. But later on the stem close to 

 the thickened base of the petiole becomes hollowed out, and in the cavity thus 

 formed little knobs arise underneath the first bud. Sometimes there is one only, 

 sometimes there are two or even three. These knobs are nothing more or less than 

 first rudiments of reserve-buds which develop in this position where they are 

 sheltered and protected by the remaining portion of the petiole. If, as is often the 

 case, in the following year the shoot put forth by the first bud dies, it falls to the 

 uppermost reserve-bud to develop into a substitution-shoot, which may perish in 

 its turn and be rejjlaced by the next reserve-bud. The different species of the 

 genus Gleditschia behave in precisely the same way as Robinia Pseudacacia, but in 

 them the reserve-buds are only partially hidden beneath the remnant of petiole, and 

 the power of forming new buds at the ends of the branches is here almost unlimited. 

 In some species of Gleditschia, e.g. G. Caspica, a substitution of shoots, one for 

 another, as they successively dry up, takes place for a period of ten or more years. 

 The consequence is that the long branches of these trees are nodulated at the seats 

 of origin of the buds, and the dried stumps of upwards of twenty short branches 

 dating from previous years are seen crowded close together on these nodes. 



In Pterocarya Caucasica, a Caucasian tree allied to the Walnut, a single bud is 

 for.med every year in the axil of each foliage-leaf, and this bud has the peculiarity 

 of being elevated from 1'5 cm. to 2 cm. above the leaf-insertion. Whilst it is 

 growing next year into a shoot, the rudiment of a reserve-bud is formed just above 

 the original leaf-insertion, but it only develops in some subsequent year in the 

 event of injury to the first shoot. 



Far more common than the above are the cases where the buds which sprout in 



