2 BUTTERWORTH, Structure of Psaroniiis. 



endogenous growth, that is without secondary thickening. 

 Certainly what is known of coal ferns points to this con- 

 clusion. I shall, however, presently put on the screen a 

 series of views which I have photographed from the 

 actual sections now lying before you, which will make 

 this matter more clear. The sections referred to above 

 showing Psaronius renaultii as Professor Williamson 

 described it, and also the sections of my new form of 

 Psaronius I have produced, so that any member may 

 examine them under the microscope. Among the slides 

 above alluded to are a few which I have copied from 

 Corda's work, to show wherein my Psaronius differs from 

 both those of Corda and that of Williamson, neither of 

 whom, I believe, hints at the possibility of the Psaronius 

 roots belonging to an exogenous fern, nor was it to be 

 expected, as no example, I believe, has ever been found 

 previous to those I shall show you, to prove that some 

 ferns, at least, show secondary growth, and may merit 

 being placed among exogenous plants. You will 

 see, as we pass the views before you, that all Corda's 

 examples, as well as that of Williamson, are of the 

 endogenous order, the vascular tissue existing in bundles 

 as in the various Rachioptera, or in lune-shaped bands as 

 seen in the main axis of Psaronius. 



In the aerial roots of the last named fern, in many of 

 Corda's examples, the central vascular axis takes the 

 shape of a star, but in my Psaronius I shall be able to 

 show you that, in several instances, a second vascular 

 tissue starts off from the above named star-shaped centre, 

 in one case entirely enclosing it in a cylinder of compact 

 secondary vascular tissue of a finer character, while, in 

 other instances, the secondary growth is only just starting 

 from the primary vascular centre. 



The roots of my new Psaronius are collected in groups, 



