SCOTS PINE. 381 



532. L. S. of Ovule with Archegonia. Split open 

 longitudinally, and dissect some of the ovuliferous scales 

 from, a second-year cone taken in June. Note that the 

 scales and the ovules have grown considerably in size. 

 Cut off the upper part of the ovuliferous scale, above the 

 ovules, embed an ovule in pith, and cut longitudinal 

 sections through it. Note (1) the tissue of the scale, with 

 vascular bundles and resin-ducts; (2) the ovule, 

 showing (3) the integument with the micropyle, within 

 which is (4) the nucellus and, within this again, (5) a 

 mass of thin- walled tissue, the endosperm or female 

 prothallus (formed by germination of the megaspore seen 

 in the nucellus of the young ovule) . (6) In the endosperm, 

 near the upper (micropylar) end, there are seen (usually) 

 two of the large oospheres, each containing numerous 

 vacuoles and covered by a layer of small cells 

 (" nutritive jacket "). 



In good sections, taken in just the right plane, note that 

 the nucellus (whose lateral portions are greatly compressed 

 and partially obliterated owing to the growth of the 

 endosperm) forms a thick apical cap over the top of the 

 endosperm ; at the top of this nucellar cap, just below the 

 micropyle, there is a cup-like depression, in which pollen- 

 grains may be seen. The pollen- tubes proceeding from 

 these grains traverse the tissue of the cap and reach the 

 upper surface of the endosperm and there widen into a 

 swelling (tip of tube) . At the top of each oosphere there 

 is a narrow neck continuous with those forming the 

 " nutritive jacket" and consisting of two or three tiers of 

 small cells the jacket represents the venter of the arche- 

 gonium ; in some cases there may be seen the nucleus of 

 the oosphere itself and at the top (just below the neck) a 

 ventral- canal-cell, which disappears at fertilisation of 

 the oosphere. 



533. Ripening Seed with Embryos, Dissect some 

 scales from the second year cone taken in August, for the 

 study of the ripening seeds ; since the integument or 

 seed-coat is now rather hard, it may be better to dissect it 

 off carefully with a knife-point or needles, After removing 



