BOTAJflCAL CONSIDERATIONS. 



15 



3, 4, 5 and 6) of the ovum development from the period 

 of its first fertilization are shown herewith. * These are 

 taken froniKruger's observations — the final (Fig. I2,6) 

 drawing shows the ultimate seed in its sac. The ovum 

 considered separately undergoes constant changes 

 even before it is fertilized. The ovule consists of a cen- 

 tral cone or nucleus (Fig. ii, it), around which 

 there are several layers of cells (Fig. ii, c, o and m). 

 The growing is around the nucleus and over it, with the 

 exception of the small opening (Fig. ii, s) or micro- 

 pyle. One cell has expanded very much at the expense 

 of the others and soon occupies the greater part 

 of the nucleus. This becomes the embryo-sac, but its 

 formation depends upon the presence of the pollen 



Fig. 16. Secliou.of seed. Vui- 17. -ippeaiance ot testa magnified. 



tubes. After they have touched the dark spot on top of 

 the nucleus, a membraneous cell wall forms around the 

 protoplastic contents of the sac; these cells divide and 

 sub-divide, and finally develop the embryo. During 

 this period, in the lower part of the embryo-sac an 

 indefinite number of minute cells are forming; these are 

 the starting points for the albumen. We neglected to 

 mention that the ovules are generally produced on the 

 outer edge of the capillary leaf: the spongy thicken- 

 ing is known as the funicle.* As the partitions or 



•Tlie alinve is only a ooniecture. Tlieiv are immerons pa«e^ of plimts 

 ■with one-cell ovary, when the ovule i< developed from tlie floral axis. 



