118 BULLETIN JARD. BOT. BUITENZORG, SÉRIE III, VOL. V, LiVR. 2. 



theory of the leaf blade is strengthened. The leaflets hâve elongated consider- 

 ably hère and they are surrounded by an epidermal layer. 



Splitting of the leaf 'Anlagen' to form the two halves of the mature ieaflet 

 occurs very early. It is possible that dissokition of the middie lamella causes 

 the séparation of the cells along the plane of the split. There is no évidence 

 of any degeneration of cells suggesting a rupture along the plane of cleavage- 



The leaflets are for a time sac-like structures. A longitudinal section 

 of such a sac is seen in Figure 42, Plate V. The cells of the sac are 

 in periclinal arrangement, five such layers can be counted in this Ieaflet. 

 The outer and innermost layers are epidermal in character. The cells 

 above and partially surrounding the Ieaflet are those of the enveloping tissue 

 (the rest of the leaf blade). This is in the form of several parallel layers 

 whose configuration conforms with the outline of the Ieaflet. Between the 

 Ieaflet and the partial outlines of tv^^o adjacent leaflets are more cells of the 

 enveloping tissue. In Figure 27, Plate 111 more of thèse leaflets are seen in rela- 

 tion to each other and to the rest of the leaf blade. Those near the apex of the 

 leaf are seen clearly imbedded in the tissue of the blade; the others. because 

 of the nature of the section, appear to be free. That, however, is not actually 

 the case since in sections like the ones represented in Figure 28 which is 

 from the next older leaf, the leaflets are still enclosed in the tissue of the blade. 



The sac-like character of the young Ieaflet is also very v^ell brought 

 out in Figures 24, 25 and 26, Plate 111. In Figure 24 the leaflets at the 

 base show various stages of progressive splitting. Figure 25 is a part of 

 a leaf, the fourteenth leaf from the growing point. Figure 22, Plate III, a 

 longitudinal section of a two year old plant, shows the position of thirteen 

 leaves. It must be remembered that the ^/g arrangement of leaves accounts 

 for the différences between the sections. Starting with the lowest plane 

 of the section we find the growing point in the form of a hémisphère, 

 the youngest leaf a conical outgrowth directly over the growing point, the 

 next leaf is represented by the two outgrowths to the left and to the right 

 of the preceding leaf. In continuing upwards we find that each successive 

 leaf is represented by one or two parts in this section. The corresponding 

 parts of a leaf whenever they occur are designated by the letters AA, BB, 

 ce, DD etc. Figure 23, Plate III is a longitudinal section through a two 

 year old plant which does not yield as many developing stages. The leaves 

 hère are numbered 1 — 1, 2 — 2, 3—3 etc. The denser areas of the figures 

 dénote the meristematic régions of the various leaves. Returning now 

 to the portion of the fourteenth leaf and bearing in mind the stage of 

 development of the several leaflets shown in the twelfth leaf, figure 22> 

 Plate 111, we can readily see that not ail the leaflets are in the same stage 

 of development at the same time. This is also brought out in Figure 24 

 of the same plate. Hère it must also be emphasized that the présence in 

 the leaf blade of a région that is adding now leaflets argues against an 

 assumption of folding of the leaf blade to form the leaflets. 



