152 Derhy — Crown Structure of Psaronius Braziliensis. 



certainly nearly mature and are at the point of fulfilling their 

 function of giving rise to a new pair of F organs, while C3 

 and C4 have still to grow considerably to attain that point. 



Figure II, which is plotted on the top face of the London 1 

 slice as a base and rises to the level of the top of the Rio slice, 

 shows a segment of the stem free from lateral organs. The 

 plant had grown above the level of the top of the stubs left by 

 the fall of Fl and F2 and was in a phase in which the P 

 organs were undergoing important changes. These consisted 

 of a subdivision into two or more parts and the appearance, 

 on their inner face, of a sprout which developed rapidly into a 

 long curved branch which soon split up into two or three parts. 

 Of these the free internal one, with the aspect of a small C organ 

 but that did not become incorporated in the magic quadrangle 

 of the C group, seem to have soon ceased to grow, since no 

 one of the four can be traced upward as far as the top of the 

 Paris slice. The proximal portion of these branches remained 

 attached to the parent organ and developed a sclerotized layer 

 on their outer face, which may be presumed to indicate that 

 they were destined to a longer life and more important 

 function than the detached parts. It seems reasonable to 

 assume that this function was the substitution of the parent 

 organ, already mature and ready to fall away, and in accord- 

 ance with this view they have been lettered Pi 7 , etc. In this 

 case, however the substitution must have been a rapid one and 

 none of the cross sections of the fossil happen to fall at the 

 proper level to give positive evidence that it actually took 

 place. 



The F3, F4 organs show a marked change of shape which 

 at the highest level (F4) had become quadrate, but otherwise 

 they had undergone no essential modification, except the 

 appearance of a few small circular markings in their central part 

 which are here interpreted as vascular strands, but which, 

 as Zeiler remarked in his description of the Paris slice, may 

 prove to be something else, — a point that can only be 

 determined by a microscopic examination that cannot be made 

 at present. The FP, F2' organs present themselves in two 

 parts which may have come from a subdivision of the original 

 sprout from the C organs, but more probably from an additional 

 sprout. These parts are still small and, except for their position 

 outside the group of C organs, present no characteristic features 

 to distinguish them from the members of that group. In the 

 case of F2' the two parts that are destined to fuse higher up are 

 aligned with detached parts of the adjacent P organs as if 

 these were destined to also take part in the future fusion. 



The older pair of C organs (Cl, C2) show subdivisions that 

 may be taken as an old age feature, since their absence in higher 



