GENUS PINUS 7 



pletely merged into an apparently single bundle. This condition, however, is never constant in a 

 Hard Pine, and a little investigation will discover a leaf with a true double bundle. 



Some cells about the fibro-vascular bundle acquire thick walls with the appearance and chemical 

 reaction of the hypoderm cells. Among the Soft Pines this condition is most obvious in the group 

 Cembroides. Among the Hard Pines it appears in all degrees of development, being absent (figs. 24, 

 25), sometimes in irregular lines above and below the bundle (figs. 26, 27, 30, 31), or forming a con- 

 spicuous tissue between and partly enclosing the two parts of the bundle (figs. 28, 29). 



The leaf-section furnishes sectional and other lesser distinctions. It is often decisive in separating 

 species otherwise diflBcult to distinguish (nigra and resinosa or Thunbergii and sinensis, etc.). Some- 

 times it is sufficiently distinct to determine a species without recourse to other characters (tropicalis, 

 oocarpa, Merkusii, etc.). An intimate knowledge of the leaf-section, with an understanding of the 

 limits of its variation, is a valuable equipment for recognizing species. 



THE FLOWERS. Plate IH, figs. 33-39. 



The fiowers in Pinus are monoecious, the pistillate in the position of a long shoot, taking the place 

 of a subterminal or lateral bud, the staminate in the position of a dwarf-shoot, taking the place of a 

 leaf-fascicle but confined to the basal part of the internode. 



Pistillate flowers are single or verticillate. On multinodal shoots they are often multiserial, ap- 

 pearing on two or more nodes of the same spring-shoot (fig. 33) . On uninodal shoots they are neces- 

 sarily subterminal (fig. 34) , the lateral pistillate flower being possible only on multinodal shoots (fig. 

 35) where it is often associated with the subterminal flower (fig. 33) . Like the multinodal shoot, on 

 which its existence depends, the lateral pistillate flower cannot be employed for grouping the species. 

 It is merely the frequent, but not the essential, evidence of a condition of growth that is more perfectly 

 characterized by the shoot itself. 



Staminate catkins are in crowded clusters, capitate or elongate (figs. 36, 37), but with much varia- 

 tion in the number of catkins in each cluster. In P. rigida I have found single catkins or clusters of 

 all numbers from two to seventy or more. In P. Massoniana and P. densiflora a cluster attains such 

 unusual length (fig. 37) that this character becomes a valuable distinction between these species and 

 P. sinensis, which has short-capitate clusters. The catkins differ much in size, the largest being found 

 among the Hard Pines. 



In the connective of the binate pollen-sacs there is a notable difference (figs. 38, 39), the smaller 

 form being characteristic of the Soft Pines. But this is not invariable (excelsa, sylvestris, etc.), and 

 the absence of complete data does not permit an accurate estimate of its importance. 



THE CONELET. Plate III, figs. 40-45. 



After pollination the pistillate flower closes and becomes the conelet, the staminate flowers wither- 

 ing and falling away. The conelet makes no appreciable growth until the following year. Like the 

 pistillate flower it may be subterminal or lateral, but a subterminal pistillate flower may become a 

 pseudolateral conelet by reason of a summer-growth (fig. 40-a). Such a condition may be recognized 

 on the branchlets of the present, and of the previous year (fig. 40-b), by the very short internode 

 and short leaves beyond the fruit. 



The conelet offers some distinctions of form, of color, and of length of peduncle, while in some 

 species (sylvestris, caribaea, etc.) its reflexed position is an important specific character. The most 

 important distinctions, however, are found in its scales, which may be 



1. entire subsection Cembra fig. 41. 



2. tuberculate tropicalis, etc fig. 42. 



3. short-mucronate . . .sylvestris, glabra, etc fig. 43. 



4. long-mucronate . . . .aristata, contorta, etc fig. 44. 



5. spinescent taeda, pungens, etc fig. 45. 



