214 Practical Plant Biology. 



PRACTICAL WORK. 



Sketch the end of a branch of Pinus silvestris, cut in June of three 

 seasons' growth, and with seed-cones attached to the terminal portions of 

 each increment. 



Cut a green cone of the preceding season down its axis with a sharp 

 knife. Sketch the smooth cut surface, showing the axis, the seed- and bract- 

 scales, and the ovules. 



Isolate a single carpel and draw it from its upper and its lower aspect, 

 showing the point of attachment, the two ovules on the upper surface, and 

 the minute bract-scale on the under surface. 



Make several median longitudinal sections of the ovules passing through 

 the micropyle. From a comparison of the clearest make out the position of 

 the integument, nucellus, female gametophyte (endosperm), and archegonia 

 with their large ova. Notice also the inroads of the male gametophytes 

 into the pointed end of the nucellus and the downward passage of pollen- 

 tubes towards the archegonia. Record these observations in drawings. 

 Estimate the actual size of the gametophytes and the ovum by means of the 

 Ghost-micrometer.- 



