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1920] ■ DUPLER—TAXUS CANADENSIS $°7 



of the seed is phylogenetically younger than the apex, where nucellus 

 and integument are free from one another, introducing a problem 

 already suggested by Strasburger (36) as to the real limits of the 

 morphological ovule. 



Integument. — The development and structure of the integu- 

 ment of T. baccata have been described rather completely by 



Strasburger (35), Bertrand (3), and Jager (15), and are not 



different in T. canadensis. The integument arises as a zone of 

 meristematic tissue surrounding the young nucellus (figs. 37-39). 

 Uniform growth in the entire zone results in a cylindrical, barrel- 

 shaped integument surrounding the young nucellus (fig. 40), and 

 extending some distance above it. At first the integument is 

 uniform in thickness, six or more cell layers thick. The integu- 

 ment is 2 -lipped from the early stages in its development, the lips 

 alternating with the upper pair of scales. This feature has led 

 some workers to interpret the integument as two carpels, and others 

 as the fusion of two sporophylls. This 2-lipped character persists 

 to the mature seed, but probably has no more morphological 

 significance than has a similar and more pronounced feature in the 

 ovules of many other conifers, especially the Abietineae, in which 

 no foliar significance is attached to this character. 



Up to the time of pollination the micropyle is relatively large 

 (fig. 40). At pollination it is filled with the pollination droplet. 

 At this time the inner wall of the integument is smooth, but soon 

 after pollination becomes closed by the centripetal radial growth 

 of a portion of the inner epidermis of two sides (figs. 41, 42, 66, 67). 

 Closure of the micropyle in this way takes place even if the ovule 

 is not pollinated, my preparations showing no difference in this 

 respect between pollinated and unpollinated ovules. Jager found 

 cases in T. baccata in which the micropyle had not yet closed at the 

 time of fertilization, although usually taking place soon after pol- 

 lination. In Juniperus both Noren (20) and Nichols (19) claim 

 the failure of micropyle closing unless pollen of Juniperus has 

 entered it, foreign pollen having no effect. Experimental data 

 on this point would be of interest. It would seem that the pollina- 

 tion droplet would be a more likely growth stimulant in this region 

 than the presence of a pollen grain on the somewhat distant nucellus, 



