to6 EXTERNAL CONFORMATION OF PLANTS. 



nation of generations, and finding its analogue in the strongly developed pro-embryo of 

 Gymnosperms and many Angiosperms. However important it may be from a scientific 

 point of view to include the different phenomena under as few general terms as possible, 

 this is iOnly useful in actual investigation when the general terms are capable of a 

 clear definition, and when they only include those things which agree jivith one another 

 in such definite properties as distinguish them at the same time from other pheno- 

 mena. I consider it, therefore, inconvenient to distinguish the differences between 

 the shoots of a plant, such as scale-shoots, foliage-shoots, and flower-shoots, simply as 

 alternations of generations. 'It would certainly be desirable to denote the fact that 

 shoots of 'a definite kind regularly produce shoots of another definite kind by a scientific 

 term. And were the term Alternation of Generations not already appropriated to the 

 phenomena we have described, it might well be applied to this purpose ; but it is not 

 applicable to both, since it would then be equivocal and therefore scientifically valueless. 

 The term Alternation of Shoots might, for instance, be applied, by analogy to this 

 particular case of metamorphosis which is of such common occurrence among Phane- 

 rogams. 



