Intrc'Iuctory . As has "been stated, the plant ineasure- 

 rr,,--^-.•^B •*:i-'-i-^ —ar.o t'-i ":,-(-•■=>■! d'^i OH t t'vo -'V'f eT^s aftei' tiie T3fi '*■■,■■■ 

 each culture irioliided stem height and leaf climensiciiG. 7rora 

 these have been derived two 2-Vv'eek data in each case, which 

 are g'vpr, in the t'^'hles, ^1) the relative rriean dallv rp.te of 

 increase in stem height per plant and (2) the relative r.ean 

 daily ra' e of increase in total leaf-product per plant, "both 

 for the t'?/c-weelr ^-ioriod. As ■""^'''-ean --n-^ -oir"^'=^^. cnt, the mean 

 daily rate ol. increase in total leaf-proiuct for a period of 

 abo'.t 4 weeks is very nearly proportional to the corresponding 

 rate of increape in actual leaf area, and it seems rafe to 

 suppose as McLean did, that the 2 -week leaf-pro'^uot values are 

 to he regarded as indices of increase in the area of t'- -. leaves. 

 Therefore one of these 2-T7eek plant values represents the stem- 

 producing po'ver of the plant ;and tlae other stands for its leaf- 

 produGJ ng power, under the given set of external conditions 

 acting duri-':'^- thp 2--,veek '-e-'-iod. Since the plants are talren to 

 be alike at the start, fseeds) these two derived plant values 

 should be the same for all individuals if all were subjected to 

 t'^^ same eff'^'^'^ive pnv' rrrr.yr.fi-itsl TonSlt'nns throughout the period, 

 and when the various plants are exposed to different environ- 

 ments the values Jib t mentioned become criteria by which the ef- 

 •f p -.*- i 'T ",;,-, Q g g Q-f f-,-op pnvi ro7-,ir,en t 'nay ^^ r>onr.,are^ with that of ail- 

 other of course -.vith reference to the particular ^et O"^ internal 

 conditions represented bj'- the plants at the beginning of the • 

 tests. T.'ie tv/o -1 an-^ "-"^ =3 just me r. ^ ' '""i ^-^ ' i-'-'^y thus Tre regarde-l 



