256 PRACTICAL BOTANY 



Pollen-grains may often be found seated on the apex 

 of the nucellus : one or more of these may throw out 

 pollen-tubes, which penetrate into its tissue. 



Dissect off one whole ovuliferous scale, and observe 

 on its upper surface, close to the base, two ovules, 

 which are anatropous. Note also the relative positions 

 of the two sets of scales. 



II. Take cones of the stage above described as (b). 



The material should be collected about the middle of June, and 

 must be hardened in alcohol. 



Strip off the ovuliferous scales of such cones : 

 the ovules will remain adherent to the base of each. 

 Cut longitudinal sections of the scales so as to pass 

 through the median planes of the ovules : mount 

 in pure glycerine, and examine with a low power. 

 Observe 



1 . The structure of the ovuliferous scale, which is 

 traversed by vascular bundles, and resin-passages. 



2. The ovule, which is united with the scale, and 

 consists, as in the younger stage, of 



a. An external integument : note the wide 

 micropyle. 



b. The nucellus as before, but larger. 



c. The embryo-sac, filled with the thin-walled 

 tissue of the endosperm. All the parts of the 

 ovule are larger than in the younger stage, but retain 

 the same relative positions. Note' carefully %'hat 

 pollen-grains (one or more) are usually to be found 

 lying on the apex of the nucellus, and that from the 

 larger cell of each of them arises a cylindrical pollen- 

 tube, which traverses the tissue of the nucellus as far 



