184< KEPRESENTATION OF 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 Coniferse three or 

 four capsular cavities the corpuscula 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. " Viscum 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 

 Orchidacese, 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. f 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 prov 

 thallium is certainly a remarkable one. It is as if in a 



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

 f Op. Cit., p. 5^1. 



