kipkxixg of seed ix gxetum. 191 



Conclusions. 



The mature structure of the seed is of interest ontog-e- 

 neticallj' as a method of closing- the pollinated oiule of a 

 gymnosperm. Further, it is of importance in coimection with 

 the comparison made in former papers* between the seeds 

 of the Gnetales and those of the Bennettitales. I do not wish 

 to draw any conclusions as to affinity, but it seems at least 

 possible that these remarkable growth (dianges in the Gnetums 

 may help us to understand these fossil seeds, and it is con- 

 ceivable tliat the different arrangements in the various species 

 of Cycadeoidea and Bennettites may be due to tlie varying 

 stages of maturity at which the seeds had arrived. 



The simple seed of WiUidinsonia Scoficaf may be 

 compared with the young seed of Gnetum. 



In the mature seeds of Cycadeoidea furriia and (' . DarfoniX 

 the micropylar tube has been regarded as part of the integu- 

 ment, but there is a break above the shoulders of the seed, 

 beyond which the micropylar tube continues as a separate 

 organ, filled with thin-walled tissue as in Gnetum. There is 

 no nucellar beak figured or described in these seeds. 



In Bennettites Moiieiei^ the upper portion of tlie 

 micropylar tube is also filled with closing tissue, and below 

 is a freely i)rojecting nucellar beak, which corresponds in 

 position and appearance with the freely projecting beak-like 

 base of the micropylar tube in G. gnenion. The space within 

 this beak-like base corresponds with Lignier's so-called pollen 

 chamber, and the small Ij'sigenous space described by him at 

 the apex of the nucellus and seen to contain pollen grains 

 corresponds in position to the pollen chamber in G. gnemon. 

 Lignier interpreted what he regarded as the single integument 

 to be a structure continuous with the micro})ylar tube. But 

 there is no detailed resemblance between their respective cell 

 organisations. It may well be that the " micropylar tube " 

 in his description represents a stopper fastened as in G. gncmori 

 to the top of the outer integument, while the projecting beak 

 is really the bioken l)ase of the micropylar tube. 



If this be the correct interpretation of B. Morierei, it would 

 bring the conflicting accounts of the various genera into line 

 with one another, while at the same time providing a parallel 

 with Gnetiim, which is at least suggestive of common 

 ancestry. 



REFERENCES. 

 BKuninoE, E. M. (1911)— 



On some points of resemhlance between Giiotalean and Bennetti- 

 talean seeds.- — Ncio Phyt., x. 

 LlGNIKR, O. (1894)— 



Vegetaiix fossiles de Xormandie. Structure et affinites du 

 licnnctt'itcs Morioei. — BiiL de la Sue. Linn, dc Xor. 



* Berrklge. 1911; Sykes. 1912; Thoday. 1911; Wiehnid. 1916. 



t Seward. 1912. 



: Wieland. 1912 (Fip:s. 6 and 11) and 1916 (p. 1.33). 



§ Lignier, 1894. 



