84 MAINE) AGRICULTURAL EXPERIMENT STATION. I904. 



During the period of receptivity of the pistil and descent of 

 the pollen tube, deep seated changes are going on in the ovary 

 which prepare the ovules for the fertilizing process. This 

 preparation consists in the formation of an organ in the nucellus 

 of the ovule called the embryo-sac, an exceedingly important 

 structure during fecundation. This embryo-sac consists of sev- 

 eral parts, which may be referred to as follows : At the micro- 

 pylar end of the sac is the egg apparatus, which consists of two 

 cells, the synergidae, and another the germ cell or oosphere, 

 which, after fertilization, becomes the embryo. At the opposite 

 end of the sac there are three cells, the antipodals, which are of 

 lesser importance. But the egg apparatus is the dynamic center ; 

 and it is supposed that this structure exerts a stimulating influ- 

 ence as the male nucleus nears its destination, the supposition 

 being that a fluid escapes from the synergidae which attracts 

 the pollen spore and unites the elements. 



In studying the approach of sexual organs Pfeffer 1 has dem- 

 onstrated that the spermatozoids of ferns are enticed into the 

 necks of the archegonia by means of malic acid ; and the arche- 

 gonia of mosses attract the spermatozoids by a solution of cane 

 sugar. Before leaving this point, reference should be made to 

 the statement of Strasburger 2 , who would explain the fusion of 

 the male and female elements as due to chemitactic and chemo- 

 tropic influences ; the explanation being that the nature and 

 strength of solutions in the pistil and in the vicinity of the ovules 

 attract or repel the pollen tubes. 



DETERMINING FACTORS, IN CASES OF ABNORMAL FERTILIZATION. 



The nature of the problem under consideration necessitates 

 the study of certain factors which may influence in some way 

 the making of the crosses. The factors here considered are : 



A. Incomplete development of pollen tubes, due to 



(1.) Impotent pollen or poisonous stigmatic fluid, or 

 (2.) Lack of nourishment of pollen tubes. 



B. Non-fusion of nuclei. 



1. Cited by Wilson. The Cell in Development and Inheritance, p. 197. 



2. Strasburger, Text-book of Botany, pp. 263, 281. 



