84 PLANT PHYSIOLOGY 



LEPESCHKIN, 1907). One may, however, assume, with NOLL, that plastic 

 stretching is also possible without exceeding the limits of elasticity. It should 

 be remembered that a stretched wooden bow unbends itself gradually, a pheno- 

 menon which is possible only in consequence of internal changes ; in this 

 unbent condition, however, the bow is capable of being again bent at any 

 moment. So also the cell-wall, stretched as a result of turgor pressure, might 

 exhibit a relaxation, i. e. even a plastic extension, without, at the same time, 

 necessitating a loss of elasticity on the part of the membrane It is often 

 assumed that the protoplasm influences the elastic properties of the membrane, 

 but there are as yet no data available to show us how that comes about. 



The possibility that the young lamellae grow actively, that is, by intus- 

 susception, is at least not contradicted by these observations ; on the other 

 hand, ASKENASY (1890) and STRASBURGER (1889) have put forward a whole 

 series of important facts in support of that view. 



265, 11. 5-8, for We are doubtless . . . outer surface, read Since growth 

 phenomena have been established also in the case of pollen grains (Oenothera ', 

 BEER, 1906), which correspond in all respects with those seen in Isoetes (comp. 

 STRASBURGER, 1907), we have obviously to deal with a phenomenon which is 

 very common in the course of origin of reproductive cells. Vegetative cells 

 behave entirely differently. In their case the membrane grows in surface 

 extent only so long as it is in contact with protoplasm, and the protoplasm 

 proceeds to form a new membrane as soon as it is separated from the wall, e. g. 

 by plasmolysis. 



1. 16, for reduced by appropriate means read transferred to an adequate 

 resistance, 



I. 17, for contracted read retracted 



II. 20-1, for exhibited growth . . . vascular bundles read complete their 

 surface-growth only after they have been relaxed by the resistance of the full- 

 grown vascular bundles. 



266, 1. 55 P. 267, 1. 12, delete If this be ... unlikely. 



267, 11. 34-7, for It does not follow . . . without a nucleus, read But this 

 is not universally true, for WISSELINGH (1904) and PALLA (1906) have definitely 

 proved the formation of membranes round non-nucleated protoplasts. 



11. 41-2, for obviously occupies . . . conception read is far removed from 

 the growing wall (KusxER, 1907). 



269, 1. 23, for built out from the spot where it originates read formed to 

 the spot which it is to occupy permanently. 



270, 1. 2, after cells), read Many Flagellata also divide longitudinally ; some 

 do so obliquely (comp. OLTMANNS, Algen, I. 48). 



1. 37 P. 271, 1. 7, delete NATHANSOHN'S . . . nucleus. 



273, 1. 17, after apex, read There are also sufficient instances of unicellular 

 organisms with bipolar structure. 



278, 1. 24, before lateral read occasional ; for both read as many 

 1. 25, for and leaves read as leaves 



279, under first cut, for Fig. 64 read Fig. 74 

 280, 1. 18, for The read These 



284, 1. 25, for (Lecture XXIII) read But it must not be supposed that the 

 law of continuity of the embryonic substance is without exception. To pre- 

 serve the general applicability of the law it would be necessary to ascribe the 



