184- REPRESENTATION 0¥ THE 



— as is illustrated in the same natural order, for within the 

 prothallial formation, or " albuminous body," above no- 

 ticed, there occur in the ovules of the Conifera? three or 

 four capsular cavities — the C07yuscula — intermediate in 

 their characters between the embryo-sacs of other Phanero- 

 gamia and the archegonia of the Cryptogamia. 



Cases are not absolutely unknown in other phanerogamic 

 orders of the presence of more than one embryo-sac in the 

 ovule. *' Visciim has two or three embryo-sacs ; these 

 may all have their germinal vesicles fertilized, and the de- 

 velopment of the embryos may go on to a certain point, 

 until one takes the lead and the others disappear."* This 

 is just what occurs in the cryptogamic spore, for though 

 -two or more of the archegonia may be impregnated, they 

 generally all abort but one. Polyembryony may occur even 

 in cases where there is but a single embryo-sac in the ovule, 

 owing probably to more than one of the contained vesicles 

 being impregnated. This is not uncommon among the 

 Orchidace^e, and also it is said in the genus Citrus, in one 

 species of which (the orange) seeds are occasionally met 

 with, containing more than one mature embryo. "[* That 

 polyembryony should be of rarer occurrence among Phane- 

 rogamia than Cryptogamia admits of a very feasible expla- 

 nation, from the difference in the mode of reproduction, for 

 one result of the enclosure of the fertilizing particles of the 

 fovilla in the pollen-tube must be to concentrate their action 

 on a single germinal focus, and prevent the impregnation of 

 any other, except in the rare case of two pollen-tubes enter-* 

 ing the same ovule. 



The last of the differential characters above mentioned 

 — the association of antheridia with archegonia in the pro- 

 thalhum — is certainly a remarkable one. It is as if in a 



* Griffith and Henfrey, Microg, Diet., p. 521. 

 t Op. Cit., p. 521. 



