BOTANICAL SUBJECTS. 197 



XI.— STIPULES, BUD SCALES, AXD COTYLEDOXS. 



What are stipules, and how do they fit into the theory that leaves 

 are modified branches ? 



If we look upon them as protectors of young tissues, we may 

 perhaps better follow the (Uscussion I have entered on in this 

 chapter. 



It is e^'ident that as long as plants remained in the condition 

 of seaweeds, they had no need of stipules as protectors. The 

 whole 2)lant then had a habit and structure suited to a water 

 surrounding. But as soon as evolution progressed, and water 

 plants began to emerge into an air surrounding, the need became 

 urgent of protecting the young tissues from dryness, heat, cold, 

 and, eventually, after becoming much modified, of protecting them 

 even from excess of moisture until they became suitably hardened. 

 So we have hairs, scales, and stipules, &c. evolving as useful 

 organs of protection, much as we have hair, wool, scales, and 

 feathers as a protection to animal tissues. In the case of stipules, 

 they may have acted in many cases, not only as protectors, but 

 also as nurses of the young leaf branches or terminal and axillary 

 buds. 



In seaweeds we meet with no part that we can call a stipule. 

 Everything there is plain sailing. We have cladophyls, and 

 sub-divisions of cladophyls. 



We begin to find something approaching to the nature of 

 stipules in ferns. We find something that might be ailed stipules 

 in Marattia, and in another ; but it is not clear what j^urpose 

 these expansions at the base of the frond petiole can serve in 

 Marattia. 



In phaeuogamous plants, however, we find whole orders ^vith 

 these appendages, whatever they may be, and we find that 

 sometimes they are the sole rei3resentatives of leaf organs. 



