826 



parenchyma, as a whole, is usually living and capable of dividing, while it 

 has died in the remaining part of the branch and is partially torn. 



It should be remarked, however, that no constant rules may be given 

 for the kind of callus formation. Often, especially in herbaceous plants, 

 the cuttings form only very little if any callus on the wound surface, swell- 

 ing out and being cut ofif by cork, but in another case the plants furnish 

 considerable masses of callus. The perfectly herbaceous summer cuttings 

 of V'itis, especially the American varieties, usually develop but little callus ; 

 sometimes, however, great masses of it. The same is true for rose cuttings, 

 if they are cut in the early spring in a vegetative soft condition, from forced 

 plants and stuck in a warm sand bed. A large supply of food and its slow 

 utilization awaken a tendency to callus excrescence. 



A work by J. Hanstein\ provided with a detailed bibliography, takes up 

 girdled cuttings. He found that such cuttings, with isolated wood and bark, 

 which had been girdled near the base, developed roots above the girdled 

 surface and not on the under cut surface. If cuttings, which had already 

 formed roots, were girdled, the further development of these roots ceased 

 and a new formation began directly above the girdled surface. An excep- 

 tion to this rule is found in all those plants in which fully developed vascular 

 bundles are found or, at least, a fully developed, sieve tube system in the 

 pith. In them despite the girdling roots are found on the under cut surface 

 of the cutting. When stating these results, we need only add that the oper- 

 ation must be carried out with ripe, or nearly ripened axes in order to obtain 

 these results. If very young herbaceous tips of woody plants are used, in 

 which also the girdling can be done cleanly only with difficulty, the new root 

 system is produced on the cut surface, or in its immediate vicinity. In this 

 all the tissues with the exception of the old prosenchyma elements participate 

 in the callus formation. The part above the girdled surface then frequently 

 dries up. The same phenomenon may be observed if cuttings are placed 

 upside down in the earth. Only infrequently do such cuttings grow further. 

 After they have formed callus and even roots on the end standing in the soil, 

 which is organically the upper end, they usually die back from above down- 

 ward to a small basal part and then develop new shoots from this. 



The results are of practical importance inasmuch as they clearly illus- 

 trate the transference of the plastic material, necessary for all new structure 

 formation. We see that the main paths for the building materials should 

 be sought in the sieve tube system in the bark. If such paths exist also in 

 the pith, a transference of the plastic substance likewise takes place there. 

 Besides these main paths there are also in cases of necessity side paths, which 

 become of importance. The parenchyma cells of the bark and pith will also 

 conduct the plastic materials upward and downward and likewise, as we see 

 in the new formation of bark on bark wounds, the medullary ray cells in the 

 axis can radially transport dissolved, reserve substances ; but the quantity 



1 Hanstein, Johannes, tjber die Leitung- des Saftes durch die Rinde, Pring-- 

 sheini's Jahrbiicher fur wissensch. Botanik, Vol. II, 1860, p. 392-467. 



