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A TEXTBOOK OF 'I'HEORETICAL BOTANY 



Fig. 1302. — Impatiens glanduligera (I. roylei). A, Micropylar end of embryo sac in longitu- 

 dinal section. Synergidae fully developed. Below them the primary endosperm nucleus. 

 The oosphere lies behind the synergidae. B and C, Transverse sections of the egg 

 apparatus. The oosphere is to the left in each case. {After Steffen.) 



at least in many plants, forming what are called " hooks " from their appear- 

 ance in longitudinal section, but which are really " hoods ", since the expan- 

 sion is all round the two cells (Fig. 1303). It is usually at this point that they 

 make contact with the embryo sac wall and consequently it is here that the 

 cytoplasmic lining of the sac terminates. The upper part of the cell wall is 

 very often marked by a system of fine cellulose fibrils, called the " filiform 

 apparatus", which is not always visible, though sometimes very conspicuous. 

 The fibrils may be parallel or radiating from the apex or they may form a 

 fine network or even a system of porose tubules {Viola) (Fig. 1304). The 

 fibrils give some reactions of cellulose, but they are not soluble in cupram- 

 monia. 



This structure has been known since 1856 but its function is not yet 



