450 OBSERVATIONS ON THE STRUCTURE 



foramen is terminal ; or more obviously, and with greater 

 certainty, where the raphe is visible, this vascular cord uni- 

 formly belonging to the outer membrane of the ovulum. 

 The chalaza, properly so called, though merely the termi- 

 nation of the raphe, affords a less certain character, for in 

 many plants it is hardly visible on the inner surface of the 

 testa, but is intimately united with the areola of insertion 

 of the inner membrane or of the nucleus, to one or other 

 of which it then seems entirely to belong. In those cases 

 where the testa agrees in direction with the nucleus, I am 

 not acquainted with any character by which it can be ab- 

 solutely distinguished from the inner membrane in the 

 ripe seed ; but as a few plants are already known, in which 

 the outer membrane is originally incomplete, its entire 

 absence, even before fecundation, is conceivable ; and some 

 possible cases of such a structure will be mentioned here- 

 after. 



There are several cases known, some of which I have 

 formerly noticed,^ of the complete obliteration of the testa 

 in the ripe seed ; and on the other hand it appears to con- 

 stitute the greater part of the substance of the bulb-like 

 seeds of many Liliaceae, where it no doubt performs also 

 the function of albumen, from which, however, it is readily 

 distinguished by its vascularity.^ But the most remarkable 

 deviation from the usual structure and economy of the outer 

 membrane of the ovulum, both in its earliest stage and in 

 the ripe fruit, that I have yet met with, occurs in Banksia 

 and Dryandra. In these two genera I have ascertained 

 that the inner membrane of the ovulum, before fecundation, 

 653] is entirely exposed, the outer membrane being even then 

 open its whole length ; and that the outer membranes of 

 the two collateral ovula, which are originally distinct, co- 

 here in a more advanced stage by their corresponding sur- 

 faces, and together constitute the anomalous dissepiment 

 of the capsule ; the inner membrane of the ovulum con- 

 sequently forming the outer coat of the seed. 



The inner membrane of the ovulum, however, in general 



' Linn. Soc. Transact, xii, p. 149. {Ante, p. 364.) ' Ibid. 



