lO Weiss, Phloein of Lepidophloios and Lepidodendron. 



and are generall}' better preserved, than the conducting 

 elements. 



We have, of course, no proof that the conducting cells 

 were actually sieve tubes, but we must remember that 

 sieve tubes are not demonstrated to exist in all living 

 LycopodiacecE. According to De Bary^ " In the larger 

 indigenous Lycopodia {L. clavaUnn and annotiniunt) there 

 occur in the vascular bundles of the stem, organs which, in 

 their position and width, have great similarity to members 

 of the sieve tubes." But the sieve plates are, usually, so 

 faint that neither he nor Hegelmaier- could find the sieve 

 plates which had been described b}' DippeP. Campbell*, 

 too, describes the sieve plates as poorly developed and 

 difficult to demonstrate. 



This absence of the sieve plates in some forms and 

 their want of distinctness in other cases must, I think, be 

 considered in connection with the chemical and physical 

 constitution of the cell wall, of the phloem elements in the 

 Lycopodia. As is known, the cell wall of the phloem 

 elements is, in these plants, not composed of cellulose but 

 of amyloid. This substance is described by Cross and 

 Bevan^ as a semi-hydrate of cellulose with the formula 

 ^(CizHaaOn) and as allied to mucilage. It is, therefore, in 

 all probability, more readily permeable than cellulose, for 

 though it has been asserted by some botanists that a 

 mucilaginous layer impedes the passage of dissolved food 

 material, Pringsheim^ states definitely that the result of 



^ De Bary. Comparative Anatomy^ p. iSl. 



* Hegelmaier. Bot. Zeitung, 1872. 



' Dippel. Ber.der-y^. Versammhtng deulscher Nalur/orscherzu Giessen, 

 1864. 



* Campbell. Mosses and Ferns, 1895, p. 473. 



^ Cross and Bevan. Cellulose, an Outline of the Chemistry of the 

 Structural Elements of Plants, 1895, p. 53 and p. 224. 



* Pringsheim. Jahrbuch fiir wiss. Bot., 1895, Bd, 28, p. H- 



