876 



hand, Hansen' describes in detail the processes of root and sprout formation 

 in Achimenes and Peperomia from the callus. In this only the first adven- 

 titious roots are produced from the already existing tissue elements. After 

 the callus tissue had increased for some time numerous pro-cambial strands 

 showed themselves in the callus, extending in all directions toward the 

 surface. Their cells soon changed into tracheae ; so that "callus"- is pro- 

 vided with a branched system of vascular bundles. Soon the peripheral 

 cells of this tissue appear to be abundantly filled with protoplasm; they 

 divide and produce a meristem which differentiates, as do the normal vege- 

 tative points, and soon an epidermis becomes very distinct. 



In the leaf cuttings of the monocotyledons, the processes of bud forma- 

 tion are the same as those in dicotyledons. Magnus'' describes bulb cuttings 

 of hyacinths. Numerous adventitious buds are formed on the ventral side 

 of the cut surface which, in case the bulb scale was still young, are produced 

 from an epidermal cell or in older scale pieces from the underlying paren- 

 chyma. At first tender knobs of tissue are formed from the dividing tissue 

 cells which continue growth at the apex in diverging cell rows; dividing 

 dichotomously. It is, therefore, actual callus. On further developed knobs, 

 a circular wall appears, developing into the first sheath-like scale of the 

 adventitious bud, while the enclosed apical cell shows growth in diverging 

 cell rows. On the bulb scales of Lilium Tigrinum and L. Auratum the buds 

 are also formed on the outer edge of the inner side. The rootlets, arising 

 on the outer side from the phloem region of the vascular bundles, live only 

 a short time since the young plant at once forms independent roots. 



The processes of bud formation in leaf cuttings do not differ essentially 

 from the voluntary production of the buds on uninjured leaves on the plant. 

 Numerous examples of these are well known*. They have been observed , 

 in mosses and ferns"', in lilies and other monocotyledons, most numerously 

 in dicotyledons. Beijerinck formed as a law for the latter, that the vascular 

 bundles of the leaf have an influence on the primordia of the adventitious 



1 Hansen, Ad., Uber Adventivbildung'en. Sitzungsber. d. phys.-med. Soc. zu 

 Erlang-en vom 14 Juni, 1880; cit. Bot. Centralbl. ISSO, p. 1001. 



2 Opportunity is here griven to call attention to the fact that the authors include 

 two different conditions under the name "Callus." 



They call tissue callus which is produced from the first cell divisions, and has 

 for some time an arrang-ement in rows; it continues growth, especially at the apex 

 of the cell rows, and lacks all differentiation. 



In the second place, however, the authors, in accordance with general usage, 

 understand by callus the structure differentiated from the callus by the production 

 of a cork zone, the formation of an inner meristem centre and the separation of a 

 ground tissue. This structure has already become similar to the tissue from the 

 wound in which it is produced. However, the juvenile conditions, distinguished by 

 apical growth, should be distinguished from these mature conditions and I propose, 

 on this account, to apply the term "callus" only to the first structures, while the 

 later stages can be known as "cicatrization tissue." 



3 Magnus, Hyacinthenblatter als Stecklinge. Sitzungsber. d. Ges. naturforsch. 

 Freunde vom 16 Juli, 187S; cit. Bot. Zeit. 1878, p. 765. 



4 Beijerinck, M. W., Over het onstaan van Knoppen en wortels uit bladen. 

 Nederl. Kruidkund. Archief. Serie II, Deel III, p. 438-493; cit. Bot. Centralbl. 1883, 

 No. 17, p. 112. 



5 Farlow, Bot. Zeit. 1874, p. ISO. — Cramer, Geschlechtslose Vermehrung des 

 Farnprothalliums, namentlich durch Gemmen resp. Konidien. Denkschr. d. Schweiz. 

 Naturforsch. Ges. XXVIII. 1880. 



