black: inflorescence and fruit of pyrus malus 533 



hand-pollinated flowers than in the flowers left to chance. A re- 

 cent article by Chittenden (2 7) emphasizes the economic im- 

 portance of the subject of pollination as well as the biological 

 significance of the problems presented by its phenomena. The 

 stigmatic surface is papillose and when it is in a receptive state is 

 moist. Germination of the pollen grain takes place immediately 

 after pollination, and fertilization quickly follows. Fertilization 

 was observed in several cases. The pollen tube, which is slender, 

 enters the micropyle of the ovule, and apparently does not break 

 down tissue to reach the egg cell. Seventy- two hours after polli- 

 nation small embryos were found, consisting of four or more cells. 

 There is great activity immediately following fertilization. 

 The embryo-sac enlarges considerably, sometimes extending 

 almost the entire length of the ovule. The endosperm nucleus 

 divides and in the free nuclear division which follows, cell walls 

 are laid down and a well-developed endosperm tissue is formed. 

 At the micropylar end the cylindrical embryo is found on a short 

 suspensor. The embryo at first is rather short and thick, but 

 soon elongates, and is always straight. Figures i and 2 in plate 

 40 show^ two embryos in different stages of development. Figure 

 I shows the younger embryo, surrounded by the endosperm, well 

 up in the micropylar end of the ovule. The small uniform cells 

 in the periphery of the endosperm are clearly differentiated from 

 the more irregular interior tissue. The cotyledons and root are 

 well defined in the embryo. The cotyledons, which are thin and 

 elongated in figure 2, show a well-defined vascular system. In the 

 root the central cylinder, cortex, and root cap are early distin- 

 guished. The blunt end of the embryo in figure 2 indicates the 

 position of the suspensor. With the development of the embryo, 

 changes have been taking place in the integuments to form the 

 brown satiny coat of the ripe seed. Pechoutre in describing the 

 development of the seed in the pear observes that the nucellus 

 and both inner and outer integuments take part in the formation 

 of the seed coat. He gives in detail the changes which occur in 

 these tissues and states that the outer integument becomes 

 organized into an inner and outer zone. A comparison of the 

 ovule in plate 39, figure i, and the two ovules in plate 40, 

 figures I and 2, indicates the gradual change in the nucellus and 

 integuments of the ovule to the seed coats. While no particular 



