222 MEMOIRS OF THE NEW YORK BOTANICAL GARDEN. 



taken as direct reactions to darkness rather than to any communi- 

 cated impulse. Transmission of the etiolative impulse is to be seen 

 in aerial shoots however. 



Aerial stems and aerial branches of plants with submerged stems 

 will be considered in a common group in the present discussion. It 

 is found that the references to etiolated stems in the greater part of 

 the literature include both forms, and that no sharp distinctions have 

 been made as to the main axis and its branches in the treatment of 

 the relation of light and darkness to plants. The amount of branch- 

 ing and prolification of stem structures of all kinds in darkness is a 

 very important feature of the reactions however and will receive at- 

 tention in the following section of this memoir. 



Effect of Darkness on Climbing Plants. — The aerial stems of 

 plants that climb by twining, and by tendrils, examined during the 

 course of my work include Apios (p. 42), Aristolochia (p. 71), 

 Bowiea (p. 82), Falcata (p. 104), Ibervillea (p. 197), Mcntspcrnmm 

 (p. 125), and Smilax (p. 199). Of these Apios and Aristolochia 

 develop stems that reach a length not far from the average nor- 

 mal, although the maximum length of stems in the open exceeds 

 that of the maximum in darkness. The average length of the in- 

 ternodes in both of the above instances was far greater in the etio- 

 lated (see pages 43 and 71 of this memoir) than in the normal. 

 Sachs found that the normal internodes of Dioscorea Batatas were 

 longer than the etiolated, that but little difference was shown by the 

 internodes in the hop vine and that etiolated internodes of Bryonia 

 dioica were slightly longer than the normal when compared with 

 regard to homologous positions in the shoot. As a result of a con- 

 sideration of the data obtained by his observations Sachs was led to 

 believe that by reason of their position in the stem some internodes 

 had become permanently etiolated or that certain internodes inherited 

 the etiolated habit, and did not undergo further elongation when 

 compelled to grow in darkness. Thus he says: " Wahrend die in 

 der vorigen Abtheilung betrachteten Internodien durch die Beleuch- 

 tung in ihren Verlangerung gehindert werden, im Finstern aber 

 ihrem Ausdehnungsstreben Geniige leisten, giebt es dagegen andere 

 Internodien, welche selbts unter der Wirkung des vollen Tageslichts 

 das Maximum ihres Langenwachstums erreichen konnen und daher 

 durch die Finsterniss keine weitere Steigerung erfahren. Solche 

 Internodien kann man gewissermassen als natiirlich etiolirte be- 



