248 



MEMOIRS OF THE NEW YORK BOTAMCAI. GARDEN. 



found to be as long as the normal in all instances, except in Meni- 

 sper7num, in which species alone the superficial measurements were 

 less than in normal stems. The epidermal cells showed an increase 

 in all dimensions in a great number of instances in which a multipli- 

 cation of these elements had also ensued. Among the earlier investi- 

 gators various contentions arose as to whether the excessive elonga- 

 tion of stems was accompanied by increase in size, or by increase 

 in number of the epidermal cells, the conclusions of the various 

 workers being based upon the small number of species examined. 

 It is to be seen however, that no general law has been discovered 

 by which the action of the epidermis in darkness may be predicated. 



a 



ODMmmm 





vymmm 





A. B. 



Fig. i68. Polygonum cuspidaium. A, partial transverse section of normal stem; 

 B, partial transverse section of etiolated stem. After Rauwenhoti. 



In SO far as the mechanical features of the epidermis are concerned 

 it is to be said that these elements, without exception, either in my 

 own work or in the experiments of previous investigators, fail to 

 attain the thickness of wall and the consequent mechanical rigidity 

 of the normal. The lack of thickening is most noticeable with re- 

 spect to the outer wall, and the ordinary cutinization and deposition 

 of secretions has not been observed in any of the species examined 

 by myself. The end walls show a tendency to lie more nearly par- 

 allel to the circumference of the stem. The epidermis, in common 

 with many other tissues, does not advance beyond a certain primary 

 stage of development, and retains the power of growth and division 



