INTRA-MICROSPORANGIAL DEVELOPMENT OF THE TUBE 

 IN THE MICROSPORE OF PINUS SYLVESTRIS. 



BY LE ROY H. HARVEY. 



The staminate inflorescences were collected in large quantities May 2, 

 1910, from a tree well exposed and from 60 to 70 years of age. The 

 material was obtained for class work in General Morphology. The cones 

 measured from five to seven mm. long and pollination probably took 

 place within the next ten days though no record was made. From one 

 to two per cent- of the microspores in all the material examined showed 

 pollen-tube development, the tube ranging in length from just-rupturing- 

 the-exine to .092 mm. In several cases two tubes were observed arising at 

 opposite poles of the microspore. 



Figure 16. Pinus laricio (after Coulter and Chamberlain). 



To bring to your attention the normal course of development of the 

 microspore I quote from Coulter and Chamberlain.^ "About May 9 (in 

 Chicago) the nucleus of the microspore of Pinus Laricio enlarges for 

 the first division (Fig. 16-D), a spindle is formed rapidly (Fig. 16-E) and 

 an equal division follows. Before the cell plate is organized, the 

 nucleus nearer to the wall of the spore begins to disorganize, and the 

 other begins to enlarge (Fig. 16-F). In this way a lenticular and dis- 

 organizing cell is cut off against the spore wall (Fig. 16-G). A second 



19th Mich. Acad. Sci. Rept., 1917. 



