I.IFR HISTORY OF PINUS I9 



lus-like bodies, of which as many as eleven have been counted 

 in a single section of a nucleus, and a less number than seven 

 is rarely found. The delicate but extensive nuclear reticulum 

 is slightly chromatic and stains scarcely more strongly than the 

 cytoplasm of the cell. Both cytoplasm and nuclear network 

 stain diffusely with gentian-violet during this period of rest 



(fig- ^)- . . . 



In those species in which the microsporangia make their 



appearance in the autumn, the pollen-sacs remain small and 

 the archesporial cells comparatively few in number until the 

 following spring. Hofmeister ('48) found the mother-cells of 

 the pollen-grains in the anthers of Pinus and Abies at the end 

 of November, Belajeff ('94) observed the pollen-mother-cells of 

 Larix in the spireme stage in October, and Coulter and Cham- 

 berlain ('01) have recently figured the ' ' microsporangium of Pinus 

 Laricio in the mother-cell stage in October." The sporogenous 

 tissue, as they have illustrated it, bears a very strong resem- 

 blance to that shown in fig. i of this paper. There is undoubted 

 evidence that these are not pollen-mother-cells in the species of 

 pines which I have studied. In the first place, the number of 

 cells in a single anther in November is far less than the number 

 of microspore-mother-cells which is eventually formed. As 

 the microsporangium enlarges in the spring these cells not only 

 increase in size but multiply in number. During the last of 

 March and first of April karyokinetic figures, representing 

 various stages of division, are seen in all preparations, and in 

 all cases division is proceeding by the typical method character- 

 istic of vegetative or somatic cells. In the latter part of April 

 or first of May (for Pimis Strobus about the middle of May), 

 typical division ceases, and, after a period of growth, the pro- 

 phases characteristic of the heterotypical division are entered 

 upon. The time at which the rest preparatory to the hetero- 

 typic mitosis begins varies by about three weeks in the different 

 species, and by ten or more days in the same species in different 

 seasons. Had Coulter and Chamberlain examined microspo- 

 rangia during the latter part of March they would doubtless 

 have found typic divisions taking place in the archesporial 

 tissue. 



