16 GENUS PINUS 



haps unfavorable season. The chances of successful germination are much increased by the inter- 

 mittent seed-release peculiar to these Pines. Such a method of dissemination must accrue to the ad- 

 vantage of a species. In other words, this intermittent dissemination and the oblique form of cone 

 with its perfected tissues all mark the highest development of the genus. 



THE SEED. Plate VI. Figs. 72-79. 



The seed of Pinus contains an embryo, with the cotyledons clearly defined, embedded in albumen, 

 which is protected by a bony testa with an external membranous spermoderm, produced, in most spe- 

 cies, into an effective wing. While the seed of other genera of the Abietineae shows no striking dif- 

 ference among the species, that of Pinus is remarkably variable, presenting alike the most primitive 

 and the most elaborate forms among the Conifers. These differences are valuable for the segregation 

 of kindred species and for some specific distinctions. 



WINGLESS SEEDS. 



"With wingless seeds the main distinction is found in the spermoderm, which is entire in one species 

 only, P. koraiensis. In P. cembra it is wanting on the ventral surface of the nut, but on the dorsal sur- 

 face, it is adnate partly to the nut, partly to the cone-scale. The nut of P. albicaulis and that of P. 

 cembroides are quite bare of membranous cover. The spermoderm of P. flexilis is reduced to a mar- 

 ginal border, slightly produced into a rudimentary wing adnate to the nut. 



THE ADNATE WING. 



In P. strobus, longifolia and their allies and in P. Balfouriana the spermoderm is prolonged into 

 an effective wing-blade from a marginal adnate base like that of P. flexilis. This adnate wing cannot 

 be detached without injury. 



THE ARTICULATE WING. 



The articulate wing can be removed from the nut and can be replaced without injury. An ineffec- 

 tive form of this wing is seen in the Gerardianae and in P. pinea, where the blade is very short and 

 the base has no effective grasp on the nut. 



The base of the effective articulate wing contains hygroscopic tissue which acts with the hygro- 

 scopic tissue of the cone-scales. The dry conditions that open the cone and release the seeds cause 

 the bifurcate base of the wing to grasp the nut more firmly. 



This articulate wing is found in P. aristata and in all Hard Pines except P. pinea, longifolia and 

 canariensis. The wing-blade is usually membranous throughout, but in some species there is a 

 thickening of the base of the blade that meets the membranous apical part in an oblique line along 

 which the wing is easily broken apart. This last condition attains in P. Coulteri and its associates 

 a remarkable development. 



Plate VI, fig. 72 shows the wingless seed of P. cembroides; fig. 73 represents the seed of P. flexilis, 

 with a rudimentary wing ; fig. 74 shows two seeds of P. strobus, intact and with the wing broken away ; 

 fig. 75 represents the articulate wing, whose bifurcate base when wet (fig. 76) tends to open and re- 

 lease the nut. "When dry (fig. 77) the forks of the base, in the absence of the nut, close together and 

 cross their tips; figs. 78, 79 show the peculiar reinforced articulate wing of P. Coulteri. 



Such wide variation in so important an organ suggests generic difference. But here we are met 

 by the association of the different forms in species evidently closely allied. The two Foxtail Pines 

 are so similar in most characters that they have been considered, with good reason, to be specifically 

 identical; yet the seed-wing of P. Balfouriana is adnate, that of P. aristata articulate. P. Ayacahuite 

 produces not only the characteristic wing of the Strobi, adnate, long and effective, but also, in the 

 northern variety, a seed with a rudimentary wing, the exact counterpart of the seed of P. flexilis. 



