Derby — Crown Structure of Psaronius Braziliensis. 151 



the cross sections at hand, taken as the top of the living 

 stem, an imaginary cut, at an angle of 45 degrees, from 

 front to back of the portion of the crown that stood 

 immediately above it. The basal planes for these figures have 

 been selected with reference to showing the three phases of 

 the plant that are represented in the material at hand, viz., 

 the stem with lateral members of the crown at its sides (I), at its 

 front and back (III) and without such members (II). 



In fig. I the basal plane is the lower face of the Strasbourg 

 slice and the inclined cut rises to the top of the London 2 slice. 

 It represents the last stage of a period of growth that termi- 

 nated with the maturing and falling away of the free portions 

 of the Fl and F2 organs whose persistent basal portions 

 are cut at about mid-length. These and the P organs may be 

 considered as constituting an old and mature crown of the 

 plant, while all the others may be referred to a new crown, or 

 crowns, in early stages of preparation. 



The two external F organs are shown rising in deep grooves 

 of the sclerotized stem rind, which, as will be seen by 

 an inspection of the corresponding cross sections in fig. 1 of 

 my preceding paper, did not close in completely behind them 

 until a higher level of growth (the interior of the London 2 

 slice) was reached. These external organs have no sclerotized 

 dermal layer. Their vascular system can be best discussed 

 in connection with that of the other pair shown in fig. III. 



The P organs, which are here also in a mature stage of 

 growth, at least so far as their stalk portions are concerned, 

 are assumed to rise flush with the stem rind and to have on 

 their outer face a sclerotized layer continuous with the stem rind 

 and destined to become incorporated with it. The justification 

 of this assumption will appear later. Three of these organs 

 present what may be considered as their normal adult character, 

 but the fourth (P3) shows an anomaly which comes from the 

 reunion of the two parts into which it was divided in its lower 

 concealed part. 



Of the members of the new crown the farthest advanced in 

 development are those constituting the front and back pair of 

 F organs, which may be considered to be at about middle age. 

 They rise just within the upper rim of the rind and have a 

 sclerotized layer on their outer face except along a median 

 keel-like portion. A future F organ (Fl'), destined to succeed 

 Fl, appears sprouting from the outer face of CI, being a 

 little in advance of its companion, which only presents itself 

 on C2 above the level of the inclined section. As will be 

 seen farther on, the members of the C group, of which only 

 the outer ones are numbered, hold a somewhat dubious 

 position between the old and new crown. Cl and 2 are 



