288 GYMNOSPERMS 



mother-cell stage is reached by the end of November. So they pass 

 the winter in the pollen mother-cell stage. 



In all of these localities the autumn and winter conditions are ap- 

 proximately the same. In warmer climates the dates would doubt- 

 less be different. We have seen a species of Finns near Jalapa, in 

 Mexico, shedding its pollen in September. It would be interesting 

 to know the life-history of such a species, with dates for the various 



l'"ic.. 291. — Piniis laricin: reduction of chromosomes in pollen mother-cells, showing 

 stages from the telophase of the first reduction division to young microspores;'*^ Chi- 

 cago (May 3); X500. 



stages. In Araucaria bidivilli, at Fresno, California, where there are 

 many large, luxuriant specimens, reduction takes place the last week 

 in March. 



In an angiosperm like Lilium, with elongated anthers, a longi- 

 tudinal section at the reduction period shows simultaneous mitosis; 

 but stages at the top, middle, and bottom may be quite different. In 

 Pinus, a section of the sporangium, in any direction, shows as wide 

 a range of stages as arc found from the top to the bottom of an anther 

 of Lilium (fig. 291). In an extremely long microsporangium, like 

 that of Araucaria, stages at the top and bottom would probably be 

 different. 



The number of chromosomes have been counted in several genera. 



