304: MORPHOLOGY OP ANGIOSPERMS 



dofilices there now seems to be little doubt. Scott has pointed 

 out that their fern-like foliage and usually mesarch bundles 

 indicate strongly a filicinean as opposed to a lycopodinean ori- 

 gin. It has further recently been shown that they are phyllo- 

 siphonic (Jeffrey 19 ), and since this feature is quite exclusively 

 characteristic of the ferns, it seems impossible to derive the 

 Cycadofilices from the Lycopods, as has been done by Renault. 2 



CYCADALES 



The leaves and fern-like habit of the Cycads afford good 

 external evidence of their filicinean origin, and their multicili- 

 ate sperms point in the same direction. The strongest evidence 

 of their having come from the ferns, however, is supplied by 

 their fibrovascular anatomy. 



Fig. Ill, R, is from a photograph of a cross-section of the 

 stem of Zamia floridana. Both pith and cortex are occupied, 

 as in Medullosa, by numerous mucilage ducts. In the cortex 

 several curved lines are present, which represent the curved 

 course of the foliar traces and are known as " girdles." Al- 

 though some years old, the fibrovascular zone is quite narrow, 

 and shows no evidence of annual rings, a feature of resemblance 

 to the Medullosae and Lyginodendron. 



In Fig. Ill, S, the central cylinder of the same species is 

 shown more highly magnified. Its continuity is obviously 

 broken by gaps, which subtend the outgoing leaf-traces. The 

 mucilage ducts of the medulla join with those of the cortex 

 through the foliar gaps. The central cylinder of Zamia, which 

 is quite typical of the Cycads in this respect, is consequently 

 phyllosiphonic. The mucilage ducts of the Cycads do not pene- 

 trate into the leaf-traces or root-steles. Hence it may be as- 

 sumed that, as in the Marattiaceae and Medullosae, they are 

 characteristic only of the extrastelar fundamental tissue. The 

 pith of the Cycads, which contains mucilage ducts continuous 

 with those of the cortex, is to be compared, therefore, with the 

 mucilaginous medulla of one of the Marattiaceae or of a Med id- 

 losa, and is to be regarded as extrastelar. 



The foliar traces of the Cycads are quite unique in struc- 

 ture and of considerable phylogenetic importance. The first 

 complete description of them was given by Mettonius. 1 As has 

 already been pointed out, the course of cycadean leaf-traces is 





