HISTOLOGY OF ANGIOSPERM STEM, BOOT, ETC. 129 



usually seen quite readily in unstained sections from fresh 

 material ; but it is perhaps better to cut across the ovaries 

 of a number of flowers and place them in alcohol or an 

 acid fixative before cutting sections, and to stain sections 

 with acetic methyl green, or iodine, or other stains. 



In T. S. of ovary note (1) the division of the ovary into 

 three chambers ; (2) the presence of vascular bundles 

 in the outer wall of the ovary and also in the partitions 

 note the six larger bundles in the outer wall, three corre- 

 sponding to the midribs of the carpels and three to the 

 outer ends of the partitions ; (3) in each chamber, where 

 the partitions meet, two anatropous ovules. 



In a single ovule note (1) the short stalk or funicle, 

 traversed by a slender bundle which comes from one of 

 the bundles in the " axile placenta " and ends in the base 

 or chalaza of the inverted ovule; (2) the two integu- 

 ments, which start from the chalaza and end at the apex 

 of the ovule in the fine canal or micropyle; (3) along 

 one side the outer integument is united to the stalk of the 

 ovule, this portion of the stalk being termed the raphe ; 

 (4) the nucellus, an ovoid mass of tissue lying within the 

 integuments and bounded above by the micropyle and 

 below by the chalaza ; (5) the embryo-sac, appearing as 

 a large cavity in the micropylar half of the nucellus. 



In the embryo-sac (examine a number of ovules in 

 order to see all these points) note (1) the vacuolated 

 protoplasm of the sac ; (2) the large central nucleus, 

 connected by protoplasmic threads with the peripheral 

 layer of protoplasm of the sac; (3)* at the micropyle end 

 of the sac, three cells forming the " egg apparatus " the 

 egg (oosphere) and the two synergids ; (4) at the oppo- 

 site end of the sac, the three antipodal cells. 



Good preparations showing the structure of the embryo - 

 sac may also be made from Marsh Marigold, White Lily, 

 etc. 



166. Pollination and Fertilisation. It is fairly easy 



to trace the passage of the pollen-tube from stigma to 



micropyle. Various plants should be tried, observations 



being made just after the flower has faded. In each case 



p. B. 9 



