10 Transactions. 



i 



Figs. 82-84 show the change in C. Cunninghamu at the base- 

 of an older plant (between first and second leaf). It will be 

 noted that there is a considerable increase in the number of 

 tracheids over a series in a younger plant (transition also 

 between first and second leaf). In the younger plant there is 

 almost constantly a single layer of tracheids on the ring ; while 

 in the same internode, if the plant has now seven or eight leaves, 

 there are two or three layers of tracheids in a similar transition 

 region. But without a great number of series it could not be 

 stated that there is a late differentiation of tracheids outside 

 the primary ring. 



After the siphonostele is attained the stem increases rapidly 

 in breadth. A well-defined endodermis is not present till the 

 stem is about T \j in. long. 



Sieve-tubes are ill defined in the first petiole, and it is only 

 after six or seven leaves have been formed that the tubes begin 

 to assume the characteristic form. Distinct sieve-tubes do not 

 appear inside the tubular stele for a considerable time. 



Fig. 43 shows typical solenostelic structure, but at once the 

 leaf-gaps begin to elongate, and persist throughout an internode. 



[In the running steins which take their origin from buds 

 formed early in the life of the plant a robust solenostele is found 

 till the runner nears the surface of the ground and leaves are 

 crowded again.] 



Change takes p'ace gradually till the mature form is reached : 

 the leaf-gaps elongate, the number of orthostichies is increased, 

 the outline of the stele becomes wavy, and the lips project 

 to give off the leaf f.v. bundles. 



The medullary bundles of the Cyatheas do not begin to be 

 formed till the pith is fairly broad. 



Near the apex, where the developing ring is still, meriste- 

 matic groups of cells are separated h}* parenchyma from the 

 ring, and these give the medullary bundles (fig. 42). 



Mucilage. 

 No signs of a mucilage system in the early stages : mucilage- 

 cells appear after the tubular stele is established ; in the petiole 

 especially they form regular rows. 



I*T7T?T 6 



Diagram showing Origin ok a Muotlagb-cbll Row. (Longitudinal 



section of Leaf. ) 



(a.) Apex of lenf. (b.) Muril:i<;o row. 



In the petiole the rows follow the protoxylciu groups rather 

 closely, the rows being generally in the bays of the vascular arcs. 



