190 



EirKXIXG OF SEED IX GXETIM. 



is just begiiiuiiig'. c is the outer covering', o is the middle 

 covering, i is tlie inner covering, terminating in the freely 

 projecting microjjylar tube, a and h are the upper and lower 

 edges of the thickened out-growing portion of the Mall of the 

 tube. The lumen of the tube is already narrowing, though it 

 is still open throughout. Into the lower edge of the thickened 

 portion at h fits the tip of the middle covering. 



Intermediate Stages. 

 The next stages in the growth and closure of the 

 micropylar tube and the development of the outer coats have 

 already been described.* 



Mature Seed. 



Fig. 2 is drawn from a mature seed, 3 cm. long, and 

 shows the thickened portion of the micropylar tube now 

 developed into a " stopper," fused on to the outer covering. 

 Its lumen is now obliterated. The outer covering during 

 ripening has carried up the stopper (s), dragging it away 

 from the middle covering, and in the process the lower portion 

 of the micropylar txibe has been broken across at its weakest 

 point above the tip of the middle covering and below the 

 stopper. The micropylar tube is tlius seen in Fig-. 2 divided into 

 two parts, the " stopper " {s) filling rip the tip of the outei^ 

 covering and adhering to it, and the " beak," or broken lower 

 portion (^). whicji projects just above the top of the middle 

 covering. The projectiiig beak is formed of hardened closing 

 tissue and its surface is rough, where it has been dragged out 

 from the gap g in the stopper. It is continuous downwards 

 with the parenchymatous basal portion of the innermost 

 covering. It will be seen that there is now^ a considerable 

 distance between the stopper and the beak, and if the mature 

 seed only were known, it would not be obvious that they were 

 part of the same structure. 



Fig. 2. — Upper portion of mature seed (3 cm long) of Q. gnemon. 



Berridge, 1911. Thoday, 1911. 



