40 



The subsections are distinguished by the position of the resinous 

 ducts within the leaf. These ducts, normally two, but very often 

 numerous, lie amid the chlorophyll-bearing parenchyma cells, 

 between the thick epidermis and the sheath which surrounds the 

 vascular bundles. When close to the epidermis the ducts are called 

 peripheral ; surrounded on all sides by the parenchyma, /^r^;Z(;/Owa- 

 tous ; close to the sheath around the vascular bundles, internal ^\xcX?>. 

 The use of this position of the ducts is the main new point in the 

 present classification. It is believed to be constant and intimately 

 connected with the essential character of the plant. The difficulties 

 attendant upon its use are ; firsts that " in some few species smaller 

 accessary ducts do occupy an abnormal position ; secondly^ that '* in 

 pines with very slender leaves it is sometimes difficult to discover 

 the ducts," and in some forms perhaps they are really absent, espec- 

 ially in cultivated specimens ; and, thirdly^ that sometimes the paren- 

 chyma separating them from the epidermis or vascular sheath is so 

 thin a layer t\idX parenchymatous ducts may be mistaken for periphe- 

 ral or inter?2aL The other distinctions though mostly more obvious 

 are less natural, only the presence or absence of hypodermal or 

 strengthening cells is difficult of appreciation and of doubtful vakie. 

 We proceed to give a somewhat abridged account of the arrange- 

 ment, but of course the students of pines will not be satisfied with 

 less than the complete monograph with all its details. Dr. 

 Engelmann includes only such species or (sub-species) as he has 

 been able to examine himself: ''the list, however, will be found 

 nearly complete." The numbers prefixed to the species are additions 

 of our own, 



SECT. I. STROBUS. 

 r. Eustrobi.~Ducts peripheral. Northern or mountain species of 



* 



the Old and New World. 

 Wings longer than the seed. 



I. P. Strobus, 2. monticola, 3. excelsa, 4. Pence, 5. parviflora, 

 6. Bonapartea, 7. Ayacahuite, 8. Lambertiana. 



** 



Wings much shorter than seeds. 



9. P. flexilis, (10. albicaulis), 11. pygmaea. 



2. Cembrae.— Ducts parenchymatous — Europe and principally Asia. 



12. P. Cembra, 13. Mandschurica, 14. Koraiensis, 



SECT. II. PINASTER, 

 A. Ducts peripheral, a. Cones subterminal. 



3. Integrifoliae.— Leaves smooth-edged, their sheaths deciduous. 



Western North America and Mexico. 



Cones short globose ; scales unarmed ; seeds large with 

 a minute wing. — Cemhroides. 



15. P. Parryana, 16. cembroides, 17. edulis, 18, monophylla. 



* 



