96 PLANT PHYSIOLOGY 



determine. BLACKMAN (1905 ; comp. also SMITH, 1906) has pointed out that 

 one agent often acts as a limiting factor and so narrows the effect of others, and 

 such limiting factors play a part in experimental investigations. Thus the 

 curve of dependence of growth on temperature may assume a quite misleading 

 form, inasmuch as from a certain point onwards the supply of the growing 

 regions with water and organic material is no longer sufficient, although it is 

 quite adequate at lower and also at higher temperatures. Graphic curves with 

 truncated apices running level for a long range must always be attributed to 

 the action of a limiting factor. 



322, 1. 20, for (III) read (Fig. 96, 7/7) 

 324, 1. 30, for 526 read 539 



326, for title of lecture read 



INTERNAL CAUSES OF GROWTH AND FORMATION 



11. 42-9, delete They stand . . . internal factor. 



327, 11. 1-3, for each other . . . functions read each other reciprocally, 

 because the specialization of one organ for the performance of a definite function 

 necessitates specialization of other organs for the carrying out of other functions, 

 although these organs may be quite capable in themselves of performing the 

 function of the first. 



11. 16-37, f or I n on ly a f ew cases . . . [MASSART, 1898] read In order to 

 study correlations it is best, in the first place, to isolate parts of the plant and 

 to determine what alterations are induced in them. One may observe in this 

 way isolated single cells or higher units such as stems, leaves, roots, or parts 

 of these. 



Plasmolysis may serve as the best means of separating a larger cell-complex 

 into its individual cells, and the results obtained are extraordinarily varied. 

 While in many plants the plasmolysed cells always rapidly die off, those of 

 others, at least if the conditions be favourable, remain alive for a long time and 

 exhibit changes of many kinds. Very commonly a new wall is excreted on the 

 outer surface of the contracted protoplasm, much more rarely growth occurs 

 before or after cell-wall formation. Cell-wall formation takes place most 

 frequently in the lower plants, but it is not unknown in Dicotyledons (MANN, 

 1906), and we may regard it as replacing the membrane from which the proto- 

 plasm has become separated as a case of regeneration. Growth after plasmo- 

 lysis has taken place appears to be limited entirely to Algae (KLEBS, 1888 ; 

 MANN, 1906). If plants are used for experiment, all of whose cells are in the 

 embryonic state, as e. g. Zygnema, the newly formed wall takes on growth, 

 just as in the old cell-wall apart from certain irregularities, it elongates over 

 its entire length. The case is otherwise with cell filaments which, like Clado- 

 phora (MiEHE, 1905), grow by means of an apical cell and hence exhibit a 

 certain contrast between embryonic and somatic cells, between base and apex. 

 After the formation of a new cell-wall round each isolated cell, there then takes 

 place an apical growth at the base of each cell leading to the development of 

 colourless undulating rhizoids ; much later on the apical end also swells, 

 becomes dark green, and develops into a normal straight-growing branch. 

 Each cell of the filament has now assumed the polarity of the entire plant and 

 becomes an independent individual. 



These observations on isolated cells introduce us to the phenomenon of 

 regeneration, essentially similar instances of which are to be met with in larger 

 portions of the plant, and we learn to recognize that they possess certain capa- 

 cities for cell-wall formation and growth which they do not exhibit when in 



