306 



Till-; SEED. 



the nucleus, or loose and cellular (as in Pyrola-seeds) , or vari- 

 ously appendaged. 



V.il. The inner coat, called TEGMKN and sometimes ENDO- 

 PLEUKA, when present is always conformed to the nucleus, and 

 is thin or soft and delicate. .Sometimes it is inconspicuous 

 through cohesion with the nucleus or with the inner surface of 

 the testa. In ovules of one coat it is necessarily wanting. 



592. Appendages or outgrowths of the testa generally have 

 reference to dissemination. Two characteristic kinds of such 



appendages are the wing and the coma. 

 both pertaining only to the seeds of dehis- 

 cent fruits and calculated, by rendering 

 seeds buoyant, to facilitate dispersion by 

 the wind. The wing of a Pine-seed (Fig. 

 661, 662) is a part of the carpellary scale 

 upon which the two ovules grew. In 

 Trumpet Creeper (Fig. 665), an entire 

 wing surrounds the body of the seed. 

 In the related Catalpa (Fig. 666), it is 

 mainly extended from the two ends, and 

 almost dissolved into a coma, the name 

 given to the tuft of soft hairs like that 

 which forms the down at one end of the 

 seed of Milkweed (Fig. 667), and of 

 Fpilobimn, and at both ends in several 

 Apocynacea?. In the Cotton-plant, very 

 long and soft hairs, admirably adapted for 

 spinning, thickly cover the whole seed- 

 666 coat. The wing and coma of seeds are 

 functionally identical with the wing and the pappus of the pericarp 

 in the samara and the akenes of Composite (">63, 564), but 

 morphologically quite unlike them. 



593. There are other (mainly microscopic) structures on some 

 seed-coats which come usefully into play in arresting farther 

 dispersion al a propitious time or place. In many but not all 

 Polemoniace;e (notably in Collomia), in certain Acanthace;e. 

 such as IJnellia tuberosa (and equally in certain Composite of 

 the Scnccio tribe and in Salvias, &c., among Labiatie. where 

 this structure is transferred to akenes and nutlets), the testa is 

 coated with short hairs, which when wetted burst or otherwise 

 open and discharge along with mucilage one or more very atten- 



Fic. r.r>r>. Winged seed of Trumpet Creeper, Tecomaradicana <;r,r,. That of Catalpa, 

 becoming cniuosr: tin- lnly iliviih'cl Irn^tlnvisi- tlm>tii,'h the embryo. 

 FIG. 667. Comose seed >1 Milkweed, Asclepias Cornuti. 



