PHYSIOLOGY OF THE RED MANGROVE. 621 



seem to radiate from a more or less definite center of growth in the 

 sac, as Cook has mentioned. This feature is seen in the figure of 

 a transverse section of the ovules. 



The function of this endosperm has engaged the attention of the 

 various botanists mentioned above. The cells themselves are large 

 and loose and are easily distinguished from those of the enclosing 

 integument and Warming^^ says they appear as if empty of con- 

 tents and that he never found starch in them, but had noticed 

 sphserocrystals and it is furthermore remarked by this author that 

 its function does not seem to be that of food storage, but its later 

 development indicates a quite unusual function. This later de- 

 velopment is the pushing out of the endosperm and the cotyledonary 

 end of the embryo through the micropylar end of the sac or what 

 now remains of it as the outer integument, into the ovarian cavity to 

 form an arillar collar or outgrowth. As Warming and Johow*^ 

 both agree, the function of this structure is not for the luring of 

 animals for the purpose of seed dissemination, as other arils in 

 MyrisHca, Casearia and Euonyinus, but, as Warming says (p. 531), 

 " Bei Rhicophora wird das extraovulare albumen wahrscheinlich 

 dazu dienen, als Saugorgan dem Keimlinge Nahrung von der Mut- 

 terpflanze zuzufiihren." This peculiar endosperm structure is seen 

 not only in the Rhizophoracese but in other viviparous plants, as 

 Treub*^ has shown for Avicennia, etc. Karsten-" has shown the 

 same conditions for R. mucronata, Brugniera, Ceriops, JEgiceras, 

 etc., and that these plants all follow the same development as was 

 early recorded by Hofmeister*^*^ in the origin of the embryo sac from 

 the nucellus, etc. Karsten divides the endosperm formation into 

 two categories ; first that form in which the embryo is soon anchored 

 near the micropyle and only after this does the endosperm, in very 

 small amounts, begin to form from unconnected cells of a foamy 

 consistency. In the second category to which Rhizophora belongs 



86 Warming, Eug., loc. cit., p. 531. 

 8" Johow, Fr., loc. cit, p. 421. 



ss Treub, M., Annalcs du Jard. Botaniquc de Buitcnzorg, Vol. 3, p. 79, 

 1882. 



89 Karsten, G., loc. cit., p. 31. 



90 Hofmeister, W., " Neuere Beobachtungen iiber Embrj-obildung bei 

 Phanerogamen," Pringshcini's Jalirb., I., p. 82, 1859. 



