Selbv: Studies in etiolation 69 



larger than in the normal, while the same gorging of the stems 

 with starch grains was noted in the perimedullary region and in 

 the medullary rays. The earlier formation of phellogen in the 

 etiolated stem may be interpreted as an adaptation to prevent dry- 

 ing out ; this phellogen was present near the summit of the etio- 

 lated stem. This precocious phellogen formation, in this case 

 with the early collapse of the epidermis, is similar to that observed 

 by MacDougal in Acer and Comics* 



Etiolated specimens with stems 50 to 60 cm. in length were 

 brought into diffuse illumination near a window and in two months 

 made an additional elongation of about 5 cm. The terminal newly 

 formed portions of such stems bore about 7 normal leaves, with 8 

 or 10 internodes immediately below still retaining the bract-like 

 organs resulting from etiolation (plate 4, figure 5). The lower 

 portion of the stem, in which precocious development of phellogen 

 had taken place, retained its brown color but was not extended, 



1 



while the entire upper portion of the stem had become green. 

 Young stems which had made but little growth in darkness made 

 much more rapid growth than that described above for the older 

 stems, and developed an equal crown of normal leaves. 



The leaves of the normal plant (plate 4, figure 6) showed a 

 single layer of palisade-cells and no stomata on the upper surface, 

 as before noted by Solereder. f The petioles showed definite 

 cambium, but the vessels gave no lignin reaction. The bract-like 

 hairy leaves of the etiolated plant (plate 4, figures 3 and 4) showed 

 no cambium in petioles, no stomata and no further differentiation 

 of the tissues than an indistinct row of palisade cells, whose 

 length and width were nearly equal. 



Rootstocks of Euphorbia corollata obtained from Ohio, were 

 also grown in light and darkness under conditions similar to those 

 for Persea. No essential difference in the rate of growth, or in 

 the total amount of tissue produced, was observed as between the 

 normal and the etiolated growths of Euphorbia (figures A and B). 

 There was noticeable variation in the thickening of the etiolated 

 stems due to an increase of cortex by activity of the cambium layer. 



* MacDougal, D. T; The influence of light and darkness u 



development (Mem. N. Y. Bot. Gard. 2:) 9l~ loo > 188-190. 1903. 



t Solereder, H. Systematische Pflanzenanatomie 774. 1900. 



