238 Practical Plant Biology. 



gametophyte of the Pine its differentiation is further reduced. The 

 reduction has also affected the megagametophyte. Instead of the 

 ovoid cellular mass found in the Pine, it retains the ccenocytic condi- 

 tion characteristic of the early stages of the female gametophyte of 

 the Pine, and even when the ovum is mature there is no cellular 

 archegonium formed for its reception. It lies in the parasitic 

 ccenocyte just like the ova of some of the parasitic Fungi. The 

 reduction in the number of the ova is also to be noticed, and the 

 fusion of the second sperm-nucleus with the fusion-nucleus and 

 that of the two polar nuclei may indicate that in these nuclei are 

 to be recognised other ova. If this interpretation is correct the 

 endosperm or food material resulting from this fusion would be 

 homologous to a second embryo. Hence, it would not be homo- 

 logous to the endosperm of the Pine. In fact, the former would 

 be homologous to a sporophyte, while the latter is homologous to 

 a gametophyte. 



PRACTICAL WORK. 



Make careful sketches of the flower of the Buttercup, viewed from above 

 and below, showing the numbers and the relative positions of the floral leaves. 



Slice the flower in two parts, beginning with the flower-stalk and passing 

 upwards through the axis. Sketch the surface so made, showing the axis and 

 flower-stalk in longitudinal section and the exact attachment of the various 

 parts. 



Isolate sepals, petals, stamens and carpels, and using a simple lens sketch 

 each from various aspects. Name the parts of the stamens and carpels. 

 Cut cross sections of the stamens and carpels in an opening bud. Mount in 

 water and cover. Sections passing through the anthers will show the four 

 pollen-sacs containing the rounded pollen-grains, the tapetal layer, the wall 

 of the sacs, the connective and its conducting tract. A drawing should be 

 made showing these parts. Sections passing through the ovary will show its 

 wall with mid-rib, its fused margins and in favourable specimens an ovule at- 

 tached to the inner surface of one of these margins. The stalk, nucellus and 

 integuments of the ovule should be made out and sketched. 



