244 MORPHOLOGY OF GYMNOSPERMS 



successive, although the former seems to be the prevaihng method; 

 and the tetrad may be tetrahedral or bilateral. The wings of the 

 spores begin to develop while they are within the mother cell (fig. 304). 

 While winged pollen grains are a feature of Abietineae, it is interest- 

 ing to note that in Pseudotsuga (156) wings do not develop, so that 

 winged and wingless pollen grains are found in the two tribes charac- 

 terized by their wings (Abietineae and Podocarpineae) . 



GoEBEL (70) has called attention to the fact that the dehiscence 

 of the microsporangia of gymnosperms is definitely related to their 

 form and position, and favors the distribution of the spores. For 

 example, the nearly related genera Picea and Abies differ in the dehis- 

 cence of their sporangia, the former being longitudinal and the latter 

 transverse. The suggested explanation is that the upright strobilus 

 of Picea requires a longitudinal dehiscence for a thorough discharge 

 of spores; while a transverse dehiscence is more effective in dis- 

 charging spores from the drooping strobilus of Abies. The Cupres- 

 sineae were considered to be outside the range of the problem because 

 their small and rather globular sporangia are not definitely oriented 

 as in the other tribes. 



THE MEGASPORANGIUM 



The ovulate strobilus of Pinaceae has given rise to more discussion 

 than any structure among gymnosperms. The great body of litera- 

 ture dealing with this subject has been traversed and outlined by 

 WoRSDELL (62), to whose account we are much indebted for the 

 following statement. The early discussions, which arose from the 

 attempt to interpret an abietineous cone in terms of an angiospermous 

 flower, have chiefly a historic interest. To decide whether such a 

 cone is a flower or an inflorescence does not seem important to the 

 modern morphologist, for if it holds any relation to these things it is 

 that of an ancestral structure which as yet has become neither flower 

 nor inflorescence. The question of chief interest is whether the ovu- 

 late strobilus of Pinaceae is to be regarded as simple or compound; 

 that is, whether the ovules are borne by axes of the first or second order. 



Among the Abietineae the ovuliferous structures (from below 

 upward) consist of a small bract, a very much larger ovuliferous 

 scale (usually becoming woody) coalescent with the bract at the very 



