1912-13.] BOTANICAL SOCIETY OF EDINBURGH 187 



ledons. Simple convolution of the cotyledons is not the 

 commonest construction of the embryo — it is, in fact, rare. 

 Its form suggests' facility of extraction in an exalbuminous 

 seed enclosed in a fruit giving restricted poral exit — but 

 that cannot be the whole adaptation. Most commonly 

 convolution is associated with that tortuous infolding of 

 the parts which is technically described as contortuplicate — 

 a condition which differs from true convolution in this, that 

 the seed-coat follows the infoldings. Almost all genera of 

 Combretaceae are described as having convolute cotyledons, 

 and the true condition is found in Terminolia and in 

 Gyrocarpus, if that be still admitted to the family. Con- 

 volution usually means auriculate cotyledonary extension 

 which more or less covers the radicle. The degree of 

 development depends on the length of embryo axis. 



In Laguncularia the special feature is that the seini- 

 macropodous axis is more than three-fourths of the length 

 of the seed and the cotyledons appear at the summit of a 

 stipe as short erect lobes, but each of them develops down- 

 wards from its margin an auricle on one side, the same side 

 in the two cotyledons, the other side showing no outgrowth. 

 The result is that the convolute part of the embryo is made 

 up of two auricles, one from each cotyledon, enwrapping 

 the hypocotyl. 



As an adaptation to specific requirements of germination 

 in correlation with the structure of the fruit the construc- 

 tion seems to suggest : when the fruit falls on the saline 

 swamp water moistens the fruit and enters through the line 

 of circumscission of the stopper which is loosened. As the 

 embryo enlarges, the elongation of the hypocotyl pushes 

 out the stopper — the construction of the fruit-wall pre- 

 cludes all rupture in other directions. Vivipary seems to 

 be excluded. 



EXPLANATION OF FIGURES. 



A, embryo entire with enwrapping cotyledonary auricles. R, tip of 



radicle. 



B, embryo from which one cotyledon has been removed and the other 



unrolled from the hypocotyl H to show its short upward elonga- 

 tion above the hypocotyl and the unilateral auricle extending 

 downwards. 



C, embryo from which one cotyledon has been cut off at Cot. 1 , and the 



auricle of the other cut off longitudinally at Cot. 2 



