THE FLOWER 359 



PRACTICAL WORK. 



(i) Cut a flower of buttercup ^ {Ranunculus) longitudinally 

 exactly down the middle with a razor or very sharp knife, and 

 draw the cut surface on an enlarged scale, showing (a) receptacle, 

 (h) calyx of sepals, (c) corolla of petals, with {d) nectaries, (e) stamens, 

 (/) carpels. 



(2) Draw under a lens a single stamen showing {a) ihe filament, 

 (6) the anther with two pairs of pollen sacs, [c) the connective 

 (continuation of the filament between the pairs of pollen sacs), 

 (d) the line of dehiscence of the anthers. Draw also a side view 

 of a carpel showing ovary and stigma. Mount a stamen and a 

 carpel in a drop of dilute gh'cerine on a slide and examine with 

 the low power. 



(3) Make a diagram of a section through a mature anther, 

 showing the four pollen sacs, in some of which two nuclei may 

 be seen, the connective traversed by a vascular bundle, and the 

 " fibrous layer " of cells between the epidermis and the cavity 

 of each pollen sac. The cells of this bear rib thickenings on their 

 walls, and it is the tension developed in this layer that splits 

 the anther open. 



Compare the section through a dehisced anther. 



(4) Remove a carpel from the old flower or young fruit of 

 Caltha (Marsh Marigold), draw the side view showing ovary and 

 stigma, and then split the ovary open so as to show the two 

 rows of ovules attached to the inner edges (towards the centre 

 of the flower), which are the joined margins (placentae) of the 

 carpellary leaf. 



(5) Under a low power draw a diagram of the transverse section 

 of the carpel of Caltha or Aquilegia (Columbine), showing the 

 closed ovary of the carpellary leaf with its midrib, and, on the 

 opposite side, its joined margins (placentae) to which the ovules 

 are attached. The section should pass longitudinally through 

 the centre of one ovule, and the side of the next belonging 

 to the other row, since the ovules of the two rows alternate. 



(5) In a section passing through the centre of an ovule identify 

 and draw carefully under the high power (a) the coats of the ovule 

 (identify if possible the micropyle, which is very narrow and may 

 not be traversed) , (6) the nucellus, (c) the embryosac with vacuolated 

 cytoplasm and conspicuous secondary nucleus, {d) the antipodal 



' If the buttercup cannot be obtained fresh, it is well to examine 

 first any fairly large fresh flower that can be obtained, draw a median 

 section through it, and then compare with the preserved buttercup 

 flower. 



