THE ANGIOSPERMAE 



1469 



Fig. 1347. — Nicotiana sp. 1-7, Development of the embryo (Solanad 

 Type). Chenopodium bonus-henriciis. 8-14, De\elopment of the 

 embryo (Chenopodiad Type). {AU after Soueges.) 



including the mycorrhizal habit, are established, produce embryos which 

 are incompletely differentiated in the seed and only develop fully after 

 germination. Such are the Balanophoraceae, Rafflesiaceae, Pyrolaceae, 

 Orobanchaceae and Orchidaceae. The pro-embryonic stages may be carried 

 out normally but development is arrested, sometimes as earlv as the four- or 

 five-cell stage, in other cases only after a multicellular body has been formed 

 but without any differentiation of cotyledons and radicle or even of the 

 primary cell-layers (Fig. 1348). 



Fig. 1348. — Epipactis pahistris. Development of the 

 embrvo up to the stage at which the seed is shed. 

 {After Treiib.) 



In Orobanchaceae this arrested development is associated with a very 

 tardy beginning of zygote division, when the endosperm is already well 

 advanced, but in Orchidaceae the endosperm development is early arrested 

 or suppressed. Although undifferentiated embryos are so constantly 

 associated with heterotrophic nutrition, this is not so invariably. For 



