CONIFERALES (PINACEAE) 283 



The other category includes the cases in which pollination and 

 fertilization occur during the same season. The records of these 

 cases show considerable variation in the time of pollination, but 

 remarkable uniformity in the time of fertilization, which falls in gen- 

 eral between the middle of June and the middle of July. The period 

 of pollen tube activity varies approximately as follows: Sequoia (92) 

 and Cryptomeria (93) about fifteen weeks; Cunninghamia (147, 180) 

 about twelve weeks; Pseudoisuga (156) about eight weeks; Tsuga 

 (60) about six weeks; Thuja (72) and Picea (79) about four weeks. 

 This perhaps fairly expresses the range of variation within a season, 

 which allows for pollination from early in January to early in June. 

 It is evident that this feature holds no relation to tribes, either in refer- 

 ence to periods of one season or of two seasons; or in reference to 

 the longer and shorter periods of the single season; nor does the time 

 of pollination seem to afifect the time of fertilization. 



The course of the pollen tube is various. Sometimes it is very 

 direct through the nucellus to the archegonia, as in Cryptomeria (93) , 

 and probably in all forms with short periods; sometimes it is devious 

 and branching, especially in forms with long periods; and in Sequoia 

 (92) the tubes penetrate between integument and nucellus, as well 

 as directly to the nucellus. In Widdringtonia (159) the solitary 

 pollen tube, after piercing the megaspore membrane, passes down 

 the surface of the endosperm for one-third to one-half its length, and 

 fertilizes the deep-seated and laterally placed archegonia (p. 271). 

 In Pseudotsuga (156) the pollen grains germinate in the outer micro- 

 pylar chamber (p. 253), and the numerous tubes pass in a tangle through 

 the inner chamber on their way to the apex of the nucellus, which 

 disintegrates in advance of the approaching tubes, so that there is little 

 or no resistance to their passage. In this case it is an interesting fact 

 that the body cell divides before the tip of the pollen tube reaches the 

 nucellus. Among the Araucarineae Thomson (107, 121) has made 

 the interesting observation that the pollen grains are lodged on the 

 ligule m Araucaria and on the bract nearer the micrcpyle in Agathis, 

 and in this position send out their tubes, which grow along the surface 

 of the ligule or bract for some distance before entering the micropyle. 

 Certain unusual occurrences in the course of spermatogenesis 

 have been observed, which may be mentioned. Coker (86) observed 



