220 



THE ANATOMY OF WOODY PLANTS 



in the case of the angiosperms, however, is different. In Fig. 164, 

 showing transverse sections of the anthers of a tulip and a honey- 

 suckle, the mechanical tissues are clearly differentiated and occupy 

 an entirely internal position precisely as in Ginkgo. There is a 

 very important difference between the situation presented by 

 the angiosperms, whether dicotyledons or monocotyledons, and 

 Ginkgo and the Abietineae. In the higher group the mechan- 

 ical tissues, constituting the so-called fiber layer of the anther 



FIG. 164. Sporangia of tulip and honeysuckle 



wall, have no longer any relation to the fibro vascular bundles of 

 the filament. In the case of the angiosperms the relation once 

 existing between the fibrovascular system and the opening mechan- 

 ism has apparently been lost. The dehiscing apparatus is, however, 

 still in a good state of development and in this respect contrasts to 

 the situation presented by the Gnetales and the higher Coniferales. 

 The structure of the walls of the microsporangia of the vascular 

 plants from Ginkgo upward is highly interesting from the stand- 

 point of the doctrine of descent. In the lower members of this 

 series the opening device of the sporangium is clearly in relation to 

 the transfusion tissue connected with the fibrovascular bundles of 

 the reproductive leaves. In the Cycadales, the lowest living seed 



