§ 1] UPON THE RATE OF GROWTH 419 



exposed to the spring sunlight were only 10 to 13 mm. high 

 — a reduction to one-fifteenth the height in the dark. Many- 

 seedlings show the same thing ; thus Sachs found that the 

 hypocotyl of the buckwheat (Fagopyrum), which attains a 

 height of 35 to 40 cm. in the dark, reaches only 2 to 3 cm. when 

 freely exposed on a sunny day — here again a reduction in 

 height of about 94%. This diminution in length is accompanied 

 for a while by a diminution in size of the plant as a whole. This 

 is shown by the measurements of Kaesten ('T1), who raised 

 kidney beans in the dark and in the light for a month or two, 

 and found that the entire individual reared during this period 

 in the light weighed less than that reared in the dark. 



The proportionate weight in dark and light was as 12 to 10, fresh weight. 

 The only organs which were heavier in the seedlings grown in the light 

 were the roots (slightly) and the leaves (as 5.4: to 1). This excess in the 

 growth of illuminated leaves as compared with those developed in the dark 

 is characteristic only of such as have broadly expanded blades. Such leaves 

 seem to require the light for their full development ; they constitute a 

 special case, the peculiarities of whose development will be considered 

 together with that of other special cases in the last Part of this work. The 

 growth of leaves, like that of the rest of the plant, is relatively retarded in 

 the daytime, but this is probably due to the increased transpiration of that 

 period (Pkantl, 73). 



The effect of daylight upon the growth of stems is, as Sachs 

 has pointed out, unequal in the different plants. In extreme 

 cases (internodes of Bryonia, a wild gourd ; of Dioscorea, the 

 yam; etc.) daylight has no evident effect, for the stems have 

 the scrawny, " etiolated " habit characteristic of plants grown 

 in the dark. Plants which are little repressed by light are 

 said by Sachs to be chiefly those whose rapidly growing parts 

 are sheltered from the sun's rays by protecting coverings. We 

 may conclude that the growth processes of such plants are 

 little interfered with by strong light, because their protoplasm 

 has through long experience become attuned to it. Except 

 where such attunement has occurred, light tends to retard the 

 growth of phanerogams. 



The germination of seeds and spores of fungi is accompanied 

 by processes akin to those of growth, and so may be treated 

 here. The germinating protoplasm of seeds is partly shielded 

 from light by a thick coat ; nevertheless a series of careful 



