THE ANGIOSPERMAE 



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bundles of the floral axis (Fig. 13 17). It is divided into uninucleate cells 

 bv transverse walls, though whether these cells should be reckoned part 

 of the endosperm is not clear. 



Fig. 13 1 7. — Myzodendron punctiihuum. A, Placenta of young fruit, flattened. Chalazal 

 tubes from the embryo sacs penetrating; the axis downwards. That on the right is still 

 non-septate. B, Older stage showing the complete tube. C, Enlarged base of a tube in 

 contact with the axial vascular tissue. {After Johnson.) 



It is not always easy to draw a line between outgrowths of the embryo 

 sac and the general swelling of the sac itself, which may encroach on the 

 surrounding tissues, as happens in Gentianaceae, especially it the swelling 

 is one-sided. The common factor in all these phenomena is that they involve 

 aggressive invasion of other tissues and the absorption of their materials, a 

 process called by Goebel " autoparasitism ". Though not confined to 

 reproductive structures, it is nowhere else so conspicuous. Its extreme is 

 reached in the ovules of Symplocarpus foetidiis (Araceae), where the endo- 

 sperm resorbs all the nucellus and integuments and is itself in turn resorbed 

 bv the embrvo, which thus comes to lie naked within the pericarp of the truit. 



