CELL MEASUREMENT 
the none too ample quantitative data concerning the effect of Hght on 
the growth and division of cells. 
The classical work on etiolation is that of Gregor Kraus,^ who made 
a large number of cell measurements in both normal and etiolated 
stems. He concluded that the greater length of etiolated internodes 
was due almost entirely to the greater length of the cells, but that a 
certain part of the increase over the normal internodes had to be as- 
cribed to an increase in the number of cells. Kraus made thousands 
of measurements, and, as a whole, his work was painstakingly done 
and of substantial value. He did not, however, make enough measure- 
ments in individual cases to establish true means, or to determine 
ranges of variation, and he likewise failed to distinguish, in measure- 
ments of epidermis, between primary and secondary cells. Moreover, 
as we shall show further on, his work must share with that of others 
the criticism that it was probably based upon material that was not 
strictly comparable. The comparability of individual plants grown 
under different conditions can only be assured by determining the 
range of fluctuating variation of a sufficient number of plants grown 
under each condition. 
The entire subject of etiolation was reviewed in 1903 by Mac- 
Dougal,^ to whose memoir the interested reader should turn for ref- 
erences to the extensive literature. With regard to the epidermal 
cells of etiolated stems his conclusion (/. c, p. 247) is as follows: 
"Epidermal cells were found to be as long as the normal in all 
instances, except in Menispermum (canadense) , in which species alone 
the superficial measurements were less than in normal stems. The 
epidermal cells showed an increase in all dimensions in a great number 
of instances in which a multipHcation of these elements had also ensued. 
Among the earlier investigators various contentions arose as to whether 
the excessive elongation of stems was accompanied by increase in 
size, or by increase in number, of the epidermal cells, the conclusions 
of the various workers being based upon the small number of species 
examined. It is to be seen, however, that no general law has been 
discovered by which the action of the epidermis in darkness may be 
predicated." Except for the explicit case of Menispermum, Mac- 
2 Kraus, Gregor. Ueber die Ursachen der Formanderungen etiolierender Pflanzen. 
Jahrb. Wiss. Bot. 7: 209-260. i869-'7o. 
3 MacDougal, D. T. The influence of light and darkness upon growth and 
development. Mem, N. Y. Bot. Gard. 2: 1-3 19. 1903. 
