554 



(Juniperus Scibino). In many trees the developmental ])eriod of a l)ranch 

 ends of itself towards the close of summer. In this a terminal bud is 

 formed which, the following spring, takes over the direct continuation of 

 the branch, as in fruit trees, oaks, ashes, spruces and hrs. In our culti- 

 vated plants the case often occurs when a second shoot (Joliaiincstrieh) is 

 developed in the same year. This not infref|ucntly produces unripe wood 

 which freezes easily in winter, while the wood of the spring shoot is always 

 completely matured. A third large group drops the tip of the branch all 

 at once in the course of the summer while unfolding, where the develop- 

 ment is otherwise perfectly normal. The continuation of the branch is 

 then taken over in the following year by the uppermost, lateral bud as 

 shown in Gymnodadus canadeyisis and Ailanthus glandulosa. I^^urther 

 examples are ofifered by the linden, the elm, the plane and the hazelnut. 

 V. Mohl proved that the trees, the tips of whose twigs almost regularly 

 freeze, belong to this last group. .S^tecimens, for example, in Rome have 

 regularly thrown off the tips of their branches in October and thus have 

 actually closed their period of gro\\th. This hapi)ens in the case oi the 

 linden. In trees of this group, which are favorites in planting, such a 

 normal ending of growth does not take place in the majority of cases. This 

 indicates that our summer is too short and too cold for them to reach full 

 development. 



Frost, therefore, always attacks immature growth. Here belong 

 Rohlna Pseudacacia, (ileditschia, Sophora japon'ica, Broussonetia papy- 

 rifera. Morns alba, Salix babylonica and Vitis v'lnifera. If the twigs are 

 to be retained, their premature defoliation would be advisable. Thus, for 

 example, according to the observations of Lawrence' in the winter of 1708- 

 1709, of all fruit trees, only the mulberry survived because its leaves had 

 been picked for feeding the silk worms some time before the occurrence 

 of the cold. 



In our fruit trees, the dying of the branch tips, as a result of the 

 occurrence of winter cold, is usually termed tip blight. Not infrequently, 

 however, a resulting ])henomenon is associated with it, which first makes 

 itself felt in summer. If it happens in many branches that only the espe- 

 cially delicate basal rings are injured, these branches, as a rule, develop 

 further and the blossom buds already formed develop fully. About June, 

 however, a yellowing pf the foliage appears, a dropping of the fruit already 

 set and a drying of the twigs. As a result of the injury to the branch ring, 

 the conducting of the nutritive substances is disturbed and the branches 

 themselves remain alive only as long as reserve substances are present. 

 After these are used up the branch dies. 



In grapevines the case in which the ^-ines freeze back to the old wood 

 deserves especial mention. There then dexelop from the base of the trunk 

 uncommonly luxuriant shoots which, it was formerly thought, would be 



Gijppert, Wiirmeeiitwirkhing', p. 



