284 Mr. J. Miers on the External Coatings of Seeds. 



hibit, in a more forcible manner than words can express, the 

 gradual extension of the placentary film, carrying within its 



Fig. 8. 



Fig. 9. 



ig- 



10. 



Fig. 11. 



expanding tissues the branches of vessels, where they find ample 

 room to spread and subdivide themselves in the manner seen. 

 This explanation is conformable with the fact, and consistent 

 with the usual rules of increment. But under the former 

 assumption, that the vessels so disposed lie within the tissues of 

 the real testa, we must suppose the annihilation of the primitive 

 placentary sheath, and the production of a fresh set of vessels 

 from the placenta, subsequent to the fertilization of the ovule, 

 which must pierce an entrance through the epiderm of the pri- 

 mine, at a point near the micropyle, and which thence distri- 

 bute themselves through the mesodermal tissue of that integu- 

 ment, — a supposition palpably absurd, and in violation of the 

 ordinary laws of mechanical growth. 



At other times, as in the Almond, the original cord of vessels 

 does not throw out dichotomizing branches from its base, as 

 shown above, but, following the expansion of the sheath, it be- 

 comes separated and distributed all round the seed into irregular 

 bundles, which extend from the hilum to the chalaza, and which 

 anastomose with one another at ganglionoid points, just as an 

 entangled skein of thread appears when pulled out by a lateral 

 strain. In Amygdalus, the arilline, testa, tegmen, and very 

 attenuated albumen, are all confluent with one another, into 

 apparently one tunic. 



Those who are not satisfied with my explanation must be 

 prepared to define upon consistent principles, which has never 

 been attempted before, how and by what means the vessels of 

 the raphe become distributed in the manner we find them. This 

 increment of the placentary sheath appears to me incontro- 

 vertible. It is, however, a consideration that concerns not only 

 the botanical, but the zoological physiologist ; for if it be true 

 that at a period immediately subsequent to the act of its fertiliza- 

 tion, the ovule becomes covered with an entire film, which pro- 

 bably exerts some yet unknown and important function towards 

 the future perfection of the embryo, it presents an exact analogy 



