290 THE AMEBIC AN NATURALIST [Vol.XLIV 



In the majority of the hard pines of the United 

 States, we find ray pits somewhat similar to those of 

 the nut pines. There are present one to eight small 

 pits in each cross-field (Fig. 2). These pits, however, 

 are very variable in size, number, form and structure. 

 In some species, and in certain regions in almost all 

 species, small piciform pits may be found (Fig. 6) oc- 

 curring with these. In most species are pits with cir- 

 cular borders of larger size and wide slit-like or lentic- 

 ular orifices (Figs. 2 and 6). In places these pits become 

 approximated and the borders fuse to form a single 

 irregular border surrounding an elongated irregular 

 pit. In certain species such as P. palustris Mill., P. 

 Murrayana A. Murray, P. tceda Linn., etc., numerous pits 

 of large size may originate in this way. These are 

 often crescentic, long oval, sausage-shaped or widely 

 lenticular in form (Fig. 6). In hard pines we see two 

 distinct lines of specialization in the formation of large 

 pits, a tendency for the piciform pits to simply increase 

 in size or a tendency for pits of large dimensions to be 

 formed from the fusion of smaller ones. Hand in hand 

 with the transition from small piciform to large pits 

 there occurs a transition from thick to thin-walled ray 

 parenchyma cells. Certain Pines (e. g., P. Murrayana 

 A. Murray) show all gradations from thick-walled cells 

 such as are characteristic of nut pines to very thin- 

 walled cells, such as occur in the rays of P. strobus 

 Linn. It is of interest to note that pit fusions take 

 place equally in both thick- and thin-walled ray ele- 

 ments. Either the thick- or thin-walled type of cell may 

 predominate in the ray of the various hard pines. In 

 the seedling and the woody axis of the cone of such 

 pines, we find the ancestral piciform type of pitting well 

 represented, and in the cone-axis in particular the ray 

 parenchyma is thick walled. 



In both the hard and soft pines there is a group char- 

 acterized by the possession of one or two very large pits 

 in each cross-field (Figs. 3 and 5). In places, however, 



