Derby — Crown Structure of Psaronius Braziliensis. 155 



tually from their point of emergence upward, giving the plant 

 its characteristic adult aspect. 



An inclined cut rising from the top of the stem across the 

 stalks of this new Cycas crown at the stage in which its 

 immature members stood erect just within the rim of the stem 

 rind would present strong analogies with that of Psaronius 

 brasiliensis as represented in fig. II, if we imagine the order 

 of the component members of the crown to be reversed so 

 that its weakest ones (the scale leaves) would stand on the 

 inner, and its strongest ones (the fronds) on the outer ring. 

 Whether this comparison has any deeper significance than that 

 of a superficial analogy, or not, is a question that must be left 

 to the botanists to decide. It has certainly been helpful in 

 the attempt to solve the riddles of Psaronius brasiliensis and 

 for this reason it has seemed worthy of being recorded here. 



Returning now to our fossil plant, it may safely be conjec- 

 tured that the strong persistent stubs of the external F organs 

 were prolonged by a tolerably large and heavy free portion 

 which extended outward obliquely and so could not be embalmed 

 in the rising stem, and that the still stronger P stalks must also 

 have had large and heavy prolongations that also bent out- 

 ward, but at too high a level above the stem top to be reached 

 before they fell away. On the other hand, the weaker C organs 

 seem to have had no free portions that were not embalmed, or 

 in other words, they retained throughout their entire life a 

 simple sprout-like character and probably at no time rose to 

 any great height above the vegetative disc. If the above com- 

 parison w T ith the immature Cycas crown be admissible, the 

 missing portion of the P stalks would correspond to the fronds, 

 those of the F organs to the flowers and the entirely preserved 

 C organs to the scale leaves. 



Thus far the stem of our plant has been considered as 

 divested of its sheath of adventitious roots, and only inferen- 

 tially has any evidence, and that of a purely negative charac- 

 ter, been evolved bearing on the original of this feature that 

 is so characteristic of the Psaronius tribe. It seems evident 

 that except sporadically (as shown by occasional root-like 

 strands traversing the rind in some of the cross sections) the 

 roots cannot be derived from the stem rind, since such an ori- 

 gin would involve an oblique, or horizontal, course in the 

 proximal portion of the middle and outer ones, whereas the 

 cross sections show them as standing vertically. The same 

 argument applies to the current hypothesis that they are derived 

 exclusively from the P organs, since this involves an oblique 

 course for about half their number in order to cover the inter- 

 mediary spaces fronting the F organs. An hypothesis, that seems 

 easily reconcilable with the view presented above of the struc- 



