CONIFERALES (PINACEAE) 253 



Taxodium (76) the ovulate strobili also begin in the early fall (in 

 southeastern United States), grow during the winter, the mother 

 cell is indistinct in March or April, and fertilization occurs in June, 

 but the seed matures before the end of the year. These two schedules 

 probably represent the extremes among Pinaceae, at least one winter 

 and not more than three elapsing between the primordium of the 

 strobilus and the shedding of the seed. So far as the investigations 

 include a record of time, the mother cells are evident and dividing 

 during the spring, from the first of March in California to the last of 

 May in England. 



The integument and nucellus are free from one another only in 

 the region of the sterile cap of the latter. In the early stages of the 

 ovule they appear almost entirely free, but the later growth of the 

 ovule is chiefly in the chalazal region, so that the free portion of the 

 two regions appears only at the tip of the mature ovule. An unusual 

 freedom of nucellus and integument is reported for the Araucarineae 

 (107), but complete freedom at the maturity of the ovule is recog- 

 nized as a primitive feature characterizing certain paleozoic seeds, 

 some of which doubtless belong to the Cordaitales. Cases of two 

 separate nucelli within a common integument have been reported 

 for Thuja (86). 



In general the integument forms a more or less elongated but in- 

 definite micropyle, but Lawson has described (156) a remarkable ' 

 organization of the micropylar tube in Pseudotsuga Douglasii. A stric- 

 ture of the integument midway between the apex of the nucellus and 

 the mouth of the micropyle results in two micropylar chambers. The 

 rim of the outer chamber is folded inward, and on the inner surface 

 of the infolded portion numerous hairhke processes are developed. 

 It is in this outer stigmatic chamber that the pollen grains lodge and 

 germinate, the pollen tubes passing through the inner micropylar 

 chamber to reach the apex of the nucellus. In Widdringtonia (159) 

 the micropylar tube is remarkably long and slender, and since the 

 integument is bilaterally winged, the ovule bears a remarkable resem- 

 blance to that of Welwitschia. 



The integument differentiates into the three layers characteristic 

 of all the groups previously considered; but the outer fleshy layer 

 does not deserve its name, for it is represented only by a thin \a-ver 



