t94 



MEMOIRS OF THE NEW YORK BOTANICAL GARDEN, 



developed. The greatest difference was to be seen in the secondary 

 wood, which consisted of much smaller elements with thinner walls. 

 The perimedullary layer was perfectly developed and the pith was 

 greater than in the normal. The influence of weak continuous 

 illumination is thus fairly similar to that of darkness, so far as the 

 central cylinder is concerned. The differentiation of the cortical and 

 epidermal systems is carried much farther in the etiolated specimen 

 examined. It is to be recalled however, that Bonnier^^^ used small 

 trees showing adult stems, while the stem described above is that of 

 the seedling, which in the normal, consisted of the first internode. 



Apios Apios. (See page 42.) 

 After the first series of observations on Apios was made, oppor- 

 tunity was afforded for an examination of the subterranean branches 

 upon which the tubers are formed by the swelling of the apical por- 

 tions of the internodes. The earlier stages of the development of 

 these formations was accompanied by the differentiation of a secon- 

 dary cambium or generative layer in the pericycle, very similar to 

 that exhibited by etiolated stems. The increase in the radial diam- 

 eter of the cortex was not readily noticeable however in the tuber- 

 forming stems. A subepidermal phellogen is formed early in the 

 tuber- forming stem, but this does not take place in the etiolated, or 

 in the normal aerial stem. Etiolated stems were free from trichomes, 

 in contrast with the subterranean tuber-forming internodes, which 

 bore these structures in great number. 



Fagus Americana Sweet. (See page 105.) 

 Young beech trees from 30 cm. to 3 meters in height were 

 brought into the control chamber and dark room in November, 

 1901. No activity was shown until July, 1902, when several buds 

 on the smaller plants began to elongate, producing branches, which in 

 some instances reached a length of 3 to 8 cm. by September i, 1902. 

 Such etiolated branches consisted of 3 to 6 internodes varying in 

 length from 4 to 15 mm. and bore minute leaves on the basal por- 

 tions and larger foliar organs on the terminal portions. The maxi- 

 mum size of these leaves was 8 cm. in width and 12 cm. in length. 

 The leaves, as well as the stems, were silky-hairy, the trichomes hav- 

 ing much the normal appearance. 



1^^ Bonnier, G- Influence de la lumiere electrique continue sur la forme et la struc- 

 ture des plantes. Rev. Gen. d. Bot. 7 : 253, 254. 1895. 



