242 MEMOIRS OF THE NEW YORK BOTANICAL GARDEN. 



soon after ; then the part falls off, and the plant, wanting its neces- 

 sary organs, perishes.'""'' 



Nearl})- all tests with the larger woody plants have been made by 

 " partial etiolations," which have been shown to secure results 

 wholly unlike those from complete exclusion from illumination. The 

 observations made by Jost on J^agiis, are the only authentic instances 

 in which proper methods were used, and his work showed most 

 conclusively that the action of light was necessary to awaken the 

 buds of this tree. It is not unlikely that the temperature may be an 

 important factor in awakening the activity of the buds of trees, and 

 that the species examined by myself might show greater activity at 

 the unknown optimum temperature in darkness. So far as the actual 

 facts are at hand however, the conclusion seems warranted that the 

 buds of Acer^ Cornus and Fagus are stimulated to activity by the 

 action of light, and that only a small proportion of the normal num- 

 ber may grow in darkness. Pofulus seems capable of carrying 

 out the activity of its buds to a much greater extent than the 

 other species in darkness. Etiolated branches do not advance 

 beyond an embryonic condition, and do not form permanent tissue, 

 enduring over a period not greater than that of an ordinary vege- 

 tative season. No previous discussion has been made of the fact 

 that all woody plants showed a tendency to develop buds on the 

 basal portion of the shoot in darkness, the terminal portions awaken- 

 ing tardily and only in small numbers, proving very refractory in 

 darkness, although appearing sound and healthy after continued con- 

 finement in the dark room. Seeds of these woody plants germi- 

 nated quite as readily in darkness as in light, the stems formed in 

 darkness being longer than those grown in light, but in no instance 

 were branches formed or the lateral buds awakened except upon the 

 destruction of the terminal bud of the main stem. The stems of 

 etiolated seedlings of this class were longer and thicker than those 

 of normal plantlets, and the internodes were longer, the number of 

 the latter not being increased in all instances. The etiolated stems 

 of seedlings showed marked variations from the normal in the man- 

 ner of development of the phellogen and generative layers. A 

 further notable feature of the etiolated stems of woody seedlings 

 consisted in the fact that the basal portions of the main stems con- 

 tained more or less permanent tissue. When the terminal portion of 



'" Hill, J. A. Anatomj of plants, p. 213. 1759- 



