1914] JEFFREY— SPORE CONDITIONS 327 



states, representing three genera. The status of some of these 

 hybrids is beyond question because the cross has been repeated 

 experimentally. Spore sterility is a marked feature in such cases. 

 A large number of examinations of normal species has been made 

 in the Polypodiaceae in the present connection, and uniformity 

 of spore-formation has been found in such cases. 



The Cycadales are of considerable interest from the evolution- 

 ary standpoint. The writer has been unable to find evidence of 

 imperfection in the mature output of the sporangium. Two species 

 of Zamia, as well as Cycas revoluta, Stangeria paradoxa, Bowenia 

 sp., and Microcycas, were all examined with unvarying results. 

 Fig. 6 shows part of a section through the microsporangium of 

 Zamia floridana. The spores appear round where seen in face 

 view, and somewhat crescentic when examined in profile. Both 

 views may be seen in the illustration. 



The monotypic Ginkgo, the sole survivor of a group once abun- 

 dant in the Northern Hemisphere, has pollen which, in the large 

 number of cases in which I have examined it, has proved to be 

 singularly free from variation in size in the same sporangium. I 

 have yet to see an imperfect microspore of Ginkgo. Fig. 7 shows 

 the pollen as seen in a transverse section of the microsporangium. 

 It will be noticed that the pollen grains present different appear- 

 ances according to the plane of section and to the angle of incidence. 

 The fact that the pollen in this interesting genus is winged as in 

 Pinus can already be seen with the magnification employed in 

 fig- 7- Fig. 8 presents a much more enlarged view, and the wings 

 can be clearly discerned. It is curious that this striking feature 

 of the pollen appears to have escaped notice. The wings bear the 

 same relation to the cells of the microgametophyte within the 

 pollen as they do in the Abietineae, and the number of prothallial 

 cells in Ginkgo corresponds with that found in the Abietineae and 

 not with the conditions found in the cycads, with which they are 

 usually more nearly associated. A contribution from this labora- 

 tory dealing with the extremely striking features of resemblance 

 between the Ginkgoales and the Abietineae will appear very shortly. 

 The resemblance extends to nearly all the more important details 

 of the reproductive and vegetative organs of the two groups. 



