86 PLANT PHYSIOLOGY 



1. 42, after may insert continue to 



I. 43, after size read (URSPRUNG, 1906 ; SCHELLENBERG, 1907). 



295, after 1. 40 read as title of new Lecture XXIII 



INTERNAL DIFFERENTIATION. ADAPTATION TO FUNCTION. 

 FACTORS CONCERNED IN GROWTH 



II. 46-7, for which often . . . end read which always begins before the first 

 has ended, but terminates after the second is complete. 



P. 296, 1. 8, for p. 7 read p. 6 



11. 19-21, for may expand . . . other elements read can only be differen- 

 tiated after reaching their full length, while, on the other hand, vessels generally 

 become differentiated before all other elements ; and as their walls are no 

 longer, or only to a limited extent, capable of growth, they exhibit special 

 arrangements which favour their passive stretching, and even their final 

 rupture. 



1. 28, after (1896) read As the embryonic cells of the growing point gradually 

 alter into permanent tissue-cells, one notices changes taking place both in the 

 cell-wall and in the cell contents. The wall takes on the final form by surface 

 growth, and assumes its characteristic sculpturing in the course of secondary 

 thickening, and also its definite chemical peculiarities. 



1. 42, after passively read (ZIMMERMANN, 1893). 



1. 52 P. 297, 1. 42, for This kind of ... Mucor. read This kind of growth, 

 which may, after KRABBE (1886), be termed ' sliding growth ', is seen most 

 clearly in elongated elements of the wood of trees, which, not infrequently, fork 

 at their ends. So long as this growth is limited to the ends of the cells, it is 

 quite comprehensible ; and by such quite local separations of the cell-walls the 

 compact tissue is loosened. Sliding growth is now known to be much more 

 widely distributed than one was at first led to suppose (NATHANSOHN, 1898 ; 

 JOST, 1901 ; STRASBURGER, 1901), and in certain situations cells must slide over 

 neighbouring cell-walls for long stretches, and whole cells must force their way 

 in between other cells whose walls were previously in contact. Since, however, 

 there is always a firm connexion between the individual elements of a tissue, 

 it is not readily seen how this sliding growth comes about. This difficulty of 

 explaining the facts cannot, however, prevent us from acknowledging the 

 existence of sliding growth. Indeed, we find that authors who previously 

 argued against it now accept it (HABERLANDT, Phys. Anat. p. 70, where other 

 good examples are given). 



According to NATHANSOHN'S statements (1898, p. 682), sliding growth 

 may take place not only between individual cells, but also between entire 

 tissues. Thus a root which has been enclosed in plaster of Paris shows, after 

 the plaster has been removed, a vigorous growth of the central and peripheral 

 parenchyma, while the reticulate vessels remain unaltered, so that the paren- 

 chyma must slide over the vascular strand. Phenomena such as these are, 

 however, obviously not very common ; but although neighbouring tissues 

 exhibit, by no means infrequently, great differences in growth activity, this does 

 not result in sliding growth, but only in a tension, known as ' tissue tension', 

 which is very common in actively-growing young tissues. 



A longitudinal tension may be easily demonstrated in solid growing inter- 

 nodes by separating, by means of a cork-borer, the pith from the peripheral 

 tissues in Sambucus, Dahlia, or Helianthus. When the borer has been with- 

 drawn, it may be seen that the pith is longer than the woody cylinder, and 

 careful measurement shows that the latter has become shorter as well as the 

 pith longer. If a median lamella, several millimetres thick, be cut out of such 



