THE STEM OF VASCULAR PLANTS. 207 



because of the coincidence of the facts, but I ought 

 to confess that the cause is unknown to me. I will 

 also add, that among Exogens similar phenomena are 

 found ; thus the leaves of the Barbary are transformed 

 into spines, and all the buds are there developed 

 into bundles of leaves; the leaves of Firs are trans- 

 formed into scaly membranes, and the axillary buds 

 are there developed into bundles of leaves. Among 

 Endogens it is the same in the Asparageae ; the abortion 

 of the leaves of Asparagus, and their changes into mem- 

 branes, cause the development of the axillary buds into 

 bundles of leaves and peduncles. The abortion of the 

 leaves of the Ruscus, and their change into membranes, 

 causes also the development of the bud into a flattened 

 branch, in form resembling a leaf, by which name it has 

 often been called ; but it is afterwards seen to bear the 

 bracts and flowers. 



The observations which I have given, tend to make us 

 conclude that the origin of the branches in Endogens is 

 not perceptibly different from that of Exogens ; but if 

 they are more seldom seen here, it arises from the mass 

 of the fibres being directed towards the summit : the 

 terminal bud is larger and stronger, since it attracts the 

 greatest part of the sap, which can only go to the lateral 

 buds when the action of the terminal one is either de- 

 stroyed by its obliteration, or balanced by the lateral 

 stagnation of the sap. But these causes of the lateral 

 stagnation of the sap are so much the more rare, as the 

 external part of the trunk is more completely hardened ; 

 which explains why woody Endogens are less frequently 

 branched than herbaceous ones. 



This last consideration leads naturally to the explana- 

 tion of one of the greatest anomalies of the growth of 

 Endogens ; viz., that some do not increase more in 

 diameter after a given term ; and that others seem to 



