258 Practical Plant Biology. 



Fucus, in which there is no spore-formation in the life-history. In 

 it reduction has been found to take place in the antheridium and 

 in the oogonium ; so that while the somatic cells of the plant are 

 diploid, this reduction secures that the gametes are haploid. The 

 diploid condition is restored by fertilisation. It is of interest to 

 note that in the position of the reducing mitosis Fucus conforms to 

 the animal scheme. 



In other plants such as Spirogyra reduction takes place in the 

 oosperm. 



These instances suffice to establish the general truth of the 

 proposition that in those plants whose life- history includes the 

 production of gametes and fertilisation a reduction-mitosis is 

 always found. The position of the reduction-mitosis in the life- 

 cycle varies in different groups. 



PRACTICAL WORK. 



Fix young buds from the flowering stem of a Turk's Cap Lily Lilium 

 martagon in a large volume of methylated spirit. Leave them to harden 

 for 24 hours. 



Cut transverse sections of buds about 5 millimetres and less in diameter. 

 Float the sections in water and select out the best and transfer them into 

 some very dilute Delafield's haematoxylin. Stain for 18-24 hours. Wash 

 the sections in a change of water and pass them through three changes of 

 spirit into oil of cloves. When the sections are quite clear lift them from the 

 oil of cloves with a needle, gently touch them against a piece of paper, to 

 remove the excess of oil, and transfer into a drop of balsam on a slide and 

 cover. 



While cutting the sections observe the six overlapping parts of the perianth 

 and the arrangement of the six stamens round the three fused carpels. In 

 the larger buds the yellow mass of pollen in the pollen-sacs is plainly visible, 

 and the fused carpels form a triangular prism in the centre of the bud. The 

 sections of this will show the three compartments of the syncarpous ovary. 

 In some of these sections will be seen ovules. Where the section passes 

 through the axis of an ovule the embryo-sac (megaspore) will be exposed to 

 view. If by good fortune the section passes through an embryo-sac during 

 the first mitosis, a stage of the reducing division will be shown. Somatic 

 mitoses will probably be found in the nucellus and in the walls of the ovary. 

 If the selection of the buds has been fortunate reducing mitoses may be found 

 in the pollen-mother-cells in the young anthers. Any mitosis observed 

 should be carefully sketched. 



Another very good source of material in which mitosis may be studied is 

 the developing seeds of the Crown Imperial Lily, Fritillaria imperialis. 

 Open the erect green fruits of this lily and take out the immature seeds when 

 they are about 5 millimetres long. Put them in methylated spirit, having 

 previously pricked the swollen central part with a needle to allow the spirit 

 to penetrate quickly. After 18-24 hours the seeds may be split in two, thus 

 opening up the enlarged embryo-sac. Remove with a needle the protoplasmic 

 lining of the sac, wash, stain, dehydrate with spirit, clear in oil of cloves and 

 mount in balsam. In the best preparations the lining of the sac is a thin 



