XX] 



ANATOMY 



103 



with large leaf-gaps. The first leaf-traces are simple strands (Fig. 398, /./. 1-6), 

 but in the later leaves the trace consists of paired strands (/./. 8). A root- 

 trace appears with some regularity related 

 to each of the early leaves. Presently 

 a vascular commissure (Fig. 398, c.s.) 

 traverses the pith linking together the 

 opposite sides of the dictyostele, and this 

 pursuing an upward course with fusions 

 at the successive leaf-gaps initiates a 

 medullary system that becomes more 

 complex upwards. This state of the 

 stelar structure, accompanied by further 

 disintegration of the dictyostele and of 

 the leaf-trace, and modified by the dorsi- 

 ventrality of the rhizome in those genera, 

 gives the relatively simple vascular system 

 of A rchajigiopteris and of Kanlfussia. I n 

 Marattia and AngiopteristhQ initial steps 

 are similar, though the final structure is 

 more complex. As the stem passes to 

 the adult state in Augiopteris three or 

 four concentric-meshed zones of vascular 

 tissue may be formed within the original 

 cylinder, giving the most complicated 

 structure recorded for the family (Fig. 

 397). From this brief description it will 

 be apparent that there is no essentia 

 difference between the Marattiaceae and 

 other Filicales as regards the origin and 

 final distribution of the vascular strands 

 in the stem, nor as regards the primitive 

 vascular arrangement in the petiole. The 

 most distinctive points which they show 

 are the high degree of the disintegration, 

 the absence of endodermis, and the origin 

 of the root-traces from the internal strands of the stem. The ontogeny 

 opens with a monostelic state and a solid xylem-core. It is in the later 

 stages that polycyclic and disintegrating complications arise; it will be 

 recognised that these vary in rough proportion to the size, and are most 

 striking in large plants oi Angiopteris. 



The vascular supply to the adult leaves originates as many distinct strands 

 from the dictyostele of the axis, and it is stated that it springs from the 



Fig. 39S. Model of the stelar sj'stem of the 

 rhizome of a young sporophyte o{ Danaea 

 a/ata Sm. /./.= leaf-traces; c.j'. = commis- 

 sure; r./. = root-trace. (After West.) 



