33^ 



FOURTH GROUP.— SEED-PLANTS. 



side there is the close affinity with the Cycadeae in which the envelope is undoubtedly 

 a true integument, and the absence of the stigma which is so characteristic a feature 

 in the ovary of the Angiosperms. This view which would prove the Gymnosperms 

 to have no title to their name, has been lately abandoned by Strasburger who was 

 once its chief supporter. Opinions also are still divided with respect to the relation 

 between the seminiferous scale and the bract-scale ; but it may be claimed for the view 

 given above and proposed before by Sachs, that it adapts itself to the facts without 

 violence and without the aid of hypotheses. Strasburger, resting on the history of 

 development and the anatomy of the parts, looks upon the seminiferous scale of the 

 Abietineae as an axial structure, a compressed branch bearing two ovules. But 

 anatomical characters cannot be used to decide morphological questions in this or in 

 any case, for their value is only secondary, and the facts of development are equally 

 compatible with the view represented above. Then in the Cupressineae and 

 Araucarieae Strasburger assumes a more or less complete coherence of the 

 seminiferous scale, which he thinks is present here, with the bract. Now in the 

 Cupressineae we simply see a luxuriant growth make its appearance after fertilisation 

 on the upper side of the scale, in the axils of which the macrosporangia are placed, a 

 growth which we are able to compare directly with that which, as I have shown, 

 covers the microsporangia on the under sic^e of the staminal leaves. That this 

 extensive growth should contain a system of vascular bundles was to be expected, 

 because their presence is in accordance with the universal rule, and they afford 

 therefore no ground for calling the growth itself a seminiferous scale. Lastly, in the 

 Araucarieae this would be a very forced explanation of the phenomena, while the view 

 that the leaf which bears the macrosporangia is a single one gives here as everywhere 

 a clear reflection of the facts ^. 



The mode in which the macrospore or embryo-sac is formed from the archesporium 

 in the Coniferae has recently been made known to us by the researches of Strasburger. 

 The archesporium in the Abietineae is a hypodermal cell, which is covered above 

 by primary tapeial cells, as in lsoeies'\ Later the archesporium is seen to be 

 sunk in the tissue of the macrosporangium, because the layers of cells of the 

 sporangium above the archesporium undergo rapid growth combined with copious 

 cell-division. In Larix then (Fig. 260 /) the archesporium divides into a lower and 

 an upper cell, and the latter again divides into two cells. The lower cell which does 

 not divide again becomes the macrospore at once without the previous division into 

 four which occurs in the rest of the Archegoniatae. It now displaces the two upper 

 cells which become disorganised, and at the same time exercises the dissolving and 

 destructive effect on the adjacent cells of the macrosporangium, which we saw, for 

 example, in the case of the macrospore of Isoeies. The young macrospore at this 

 stage of its existence, which is reached at different times in different genera, lies 

 therefore free in the loosened cells of the tissue of the macrosporangium. In other 

 cases, as in Ctipressm sempej-virens and Callitris qtiadrivalvis (Fig. 259), the arche- 





^ [Dickson, in Trans. Bot. Soc. Edin. xvi, 1885, gives a useful resume of the views which have 

 been advanced respecting the morphology of the parts of the cone, adhering to Baillon's hypothesis 

 that the seminiferous scale is a cladode and the integument an ovary. 



^ See page 294; and with regard to the 'primary tapetal cell,' see the note under development 

 of pollen-sacs in Angiosperms on page 363.] 



