



\c 



LIFE HISTORY OF PINUS 7 1 



found fully organized and nearly ready for the reception of the 

 pollen-grains (figs. 122, and 123). The evidence is conclusive 

 that the ovules are not organized in the species of pines 

 studied by the writer until about three weeks or less before 

 pollination, and seven months later than in Pinus Laricio as 

 recorded by Coulter and Chamberlain. This is the more surpris- 

 ing when we -consider that P. austriaca is at least a variety of 

 P. Laricio , and, according to some authorities, it is a synonym 

 for that species. 



It is not my purpose to enter into a discussion of the origin 

 and cellular development of the female cone, nor yet of the 

 homologies of its parts. These points have been fully investi- 

 gated by Celakovsky, who has frequently published papers on 

 this subject from 1879 to the present time, and the many theories 

 advanced by different writers regarding these structures have 

 recently been brought together and reviewed by Worsdell ('oo). 



FORMATION OF THE AXIAL ROW. 



The Macros-pore-mother-celL The origin of the sporog- 

 enous tissue from a hypodermal cell or cells was described by 

 Strasburger for several Gymnosperms in 1879, an( * this idea 

 without further confirmation has come down to the present time. 

 While this may be true for many Gymnosperms, and possibly 

 for Pinus, I find no evidence, direct or indirect, that the macro- 

 spore-mother-cell is derived from a hypodermal cell in the pines 

 investigated. When the mother-cell is sufficiently differentiated 

 to be distinguishable from the other cells of the surrounding tissue, 

 it is found to lie deep within the nucellus ; and there are no rows 

 or axial strands of cells lying above it to suggest its derivation 

 from a hypodermal cell. On May 8, 1902, the ovules of Pinus 

 rigida were sufficiently developed to show clearly the separation 

 into nucellus and integument, and a like condition was found to 

 exist in P. Strobus on June 6, 1898. In both instances, so 

 far as one is capable of determining, every cell of the nu- 

 cellus is exactly like every other cell (fig. 123), and the 

 same condition obtains in the other species at this time. One 

 week later, as illustrated for Pinus rigida^ the macrospore- 

 mother-cell can first be distinguished, and the so-called spongy 



