BOTANICAL SUBJECTS. 141 



CONCLUSION. 



Then, after all this discussion, which threatened to become 

 interminable, the reader might ask. What is the upshot ? 

 In a few words the inevitable conclusion is : — 

 (a.) That in the passage of plants from a water to an air 

 medium, the cladophyl or frond of seaweeds has become 

 the leaf of land plants, with its infinite modifications of 

 texture, &c. 

 (b.) That the midrib of Delesseria coriifolia, in turning, by 

 decay of the lamina, into a stem, shows us that the 

 midrib of the leaves of flowering plants is nothing but a 

 stem, and that there is no morphological distinction 

 between the cladophyls of land plants and their leaves. 

 (c.) That it is the commonest phenomenon in seaweeds for the 

 margins of their leaves to give forth branches, and 

 that the atrophy or non-development of the latter is 

 represented by marginal teeth, both in seaweeds and 

 ph^enogams. 

 This being so, it follows that the teeth of phaenogamous leaves 

 represent atrophied branches. In other words, the stem of a ]3lant 

 corresponds to the midrib* of its leaf ; the leaf is to the stem 

 what a tooth is to the leaf. When a leaflet atrophies it becomes 

 a tooth, as in Vicia hirsuta (Fig. 36), and when a leaf atrophies 

 it also becomes a tooth, as in the depauperized leaves of Ruscics ; 

 although the leaflet and leaf are transformed into teeth, they do 

 not always lose the power of giving off buds (branchlets) from 

 their axilla, such as are those of Xylophylla and Rtiscus. 



* The gnarly and crooked stem of an old oak certainly does not look like 

 the midrib of one of its leaves. Age and the old bark have masked the 

 stem's identity with the midrib. 



