Spermatophytes Gymnosperms 



259 



The period at which the various stages may be found varies 

 with the species, the locality, and the season. In Pinus Laricio 

 the megaspore mother cells appear as soon as the young strobili break 

 through the bud scales. At Chicago, in the season of 1897, material 

 collected May 27 did not 

 yet show archegonia; the 

 ventral canal cell was cut 

 off about June 21 (see 

 Fig. 90), the fusion of the 

 egg and sperm nuclei 

 occurred about a week 

 later, and stages like 

 Fig. 89, B, C, and D, 

 were common in material 

 collected July 2. In the 

 season 1896 all the stages 

 appeared about two 

 weeks earlier. In Pinus 

 sylvestris the stages ap- 

 peared a little earlier 

 than in Pinus Laricio. 



After the stage shown 

 in Fig. 89, A, has ap- 

 peared, it is necessary to 

 collect every day until 

 the stage shown in 

 Fig. 89, D, is reached. 

 If collections are made at 

 intervals of 3 or 4 days, 

 the most interesting 

 stages, like the cutting 

 off of the ventral canal 



X. 



FIG. 91. Pinus Banksiana: photomicrograph of 

 young embryos teased out by the method described 

 in the text; from a preparation by Mr. J. T. 

 Buchholz; Cramer contrast plate; 16mm. objective; 

 no ocular or Abbe condenser ; camera bellows , 75 cm. ; 

 safranin filter; arc light; exposure, 17 seconds. Xo4. 



cell, fertilization, and the 



first divisions of the nucleus of the oospore, may be missed altogether. 

 It should be mentioned that all the ovules of a cone will be in very 

 nearly the same stage of development; consequently it is worth 



