8 BULLETIN 844, TJ. S. DEPARTMENT OF AGRICULTURE, 



mature pollen grains is vacuolate, and it contains a fatty oil in the 

 form of an emulsion. Soon after the pollen grains are formed, the 

 walls of the mother cells disappear, thus permitting the pollen grains 

 to lie loose in the anther. 



FERTILIZATION IN MELILOTUS ALBA. 



The time intervening between pollination and fertilization was 

 investigated with both self-pollinated and cross-pollinated flowers. 

 In cross-pollination the parents, were separate plants. This point 

 was investigated with plants out of doors during the summer of 1916 

 and with plants in the greenhouse during the following winter. The 

 time elapsing between pollination and fertilization ranged from 50 to 

 55 hours and was not longer in the case of self-pollinated than with 

 cross-pollinated flowers. Furthermore, the rate of the development 

 of the embryo in each kind of pollination was studied and was found 

 to be as rapid in self-pollination as in cross-pollination. Therefore, 

 self-pollination is apparently as effective as cross-pollination in 

 Melilotus alba so far as the vigor of pollen tubes and the rate at which 

 embryos develop are concerned. Melilotus officinalis was not studied 

 in reference to this point. 



Considerable difference often exists in the size of the young embryos 

 in the ovules of the same pod. This is due in part to a difference 

 in the time of fertilization, although some of it is due to a difference 

 in nourishment. It was observed that the ovule first fertilized 

 might be an upper one, lower one. or any one between these. Occa- 

 sionally one or more ovules are not fertilized. 



DEVELOPMENT OF THE SEED. 



A proembryo with a rather long suspensor is developed from the 

 fertilized egg. (PL II, fig. 2.) The endosperm, which quite early 

 forms a peripheral layer around the entire embryo sac, develops most 

 rapidly about the embryo, which soon becomes thoroughly embedded 

 in it. (PL III, figs. 1 and 2.) After the embryo has used up the 

 endosperm in the micropylar end and has enlarged so much as to 

 occupy nearly all of the space in this region, the development of the 

 endosperm becomes more active in the chalazal end, .and when the 

 embryo is mature there is very little endosperm left. 



The seed coat begins to form about the time of fertilization, 

 although it apparently does not depend upon it, for in ovules where 

 fertilization is prevented the outer integument undergoes the early 

 modifications in the development of the seed coat before the ovule 

 breaks down. The development of the seed coat is apparent first at 

 the micropylar and chalazal ends, where the outer cells of the outer 

 integument become much elongated and their outer walls thicken 

 very soon after fertilization. The modifications in the development 



