FERTILIZATION 151 



True chalazogamy, therefore, has as yet been found only 

 among the Amentiferae, but such an intermediate condition 

 as shown by Ulmus, Cucurbita, and Alchemilla, in which the 

 pollen-tube enters the ovule at the chalazal end, but traverses 

 the integument instead of the nucellus, suggests that chala- 

 zogamy is an exceptional condition derived from the ordinary 

 route of the pollen-tube through the micropyle. In certain 

 cases the tube reaches the micropyle by passing along more or 

 less of the surface of the integument; in other cases it enters 

 the tissues of the integument, and finally it penetrates deeper, 

 entering the chalazal tissue. This seems to be a natural 

 sequence of events that resulted in chalazogamy, which there- 

 fore \vould hold no relation to a primitive condition of Angio- 

 sperms or to their classification. 



In passing through the micropyle the pollen-tube is more 

 or less compressed, and upon reaching the wall of the embryo- 

 sac may broaden out upon it. In some cases (p. 94) the 

 synergids have already pierced the wall of the embryo-sac, but 

 in most cases it must be pierced by the tube. Upon entering the 

 sac the tube either passes between the synergids, as in Ponte- 

 deria (Smith 28 ), Euphorbia (Lyon 29 ), sometimes Salix 

 (Chamberlain 23 ), etc. (Fig. 44) ; or between the sac-wall and 

 one synergid, as in Alisma (Schaffner 22 ), Lilium (Coulter 25 ), 

 Ranunculus (Coulter 27 ), Fagus (Benson 15 ), Silphium (Mer- 

 rell 35 ), etc. Recently, however, Guignard 56 has reported that 

 in Nicotiana Tabacum and Datura laevis the tube passes into 

 a synergic! and discharges its contents into the broken-up body. 

 So far as our own observation goes, the usual route of the tube 

 is between the sac-wall and one of the synergids, but this may 

 well vary even in the same species. Within the sac the tip 

 of the tube usually becomes much swollen, often appearing 

 pouch-like, as in Alisma, Erythronium, Ranunculus, Silphium, 

 etc., due probably to the rapid absorption of material from the 

 synergid. As a rule, one synergid is disorganized by its contact 

 with the tube; but in Salix (Chamberlain 23 ) (Fig. 44), Sil- 

 pliium (Merrell 85 ), Nigella (Guignard 53 ), etc., cases of fer- 

 tilization have been observed in which both synergids remained 

 intact; while in Erigeron (Land 38 ) both synergids are fre- 

 quently disorganized. D'Hubert 17 has made the interesting 

 observation in connection with his study of the Cactaceae that 

 11 



