( 266 ) 



On the Analogy between the mode of Reproduction in Plants 

 and the '* Alternation of Generations^ observed in some 

 Badiata. 



The very remarkable fact that a Polyp and a Medusa may 

 be in some instances different states of one and the same 

 species, has been well established of late by the researches of 

 Sars, Dalyell, Steenstrup, and others ; and recent important 

 observations have been made on the subject by Professor 

 Agassiz. The alternations are as follows : — ■ 



1. The Medusa produces eggs : — 



2. The eggs, after passing through an infusorial state, fix 

 themselves and become polyps, like Corynse, Tubulariae, or 

 Campanularise : — 



3. The polyps produce a kind of bud that finally drops ofi^ 

 and becomes a Medusa. 



Thus the egg of a Medusa, in such cases, does not produce 

 a Medusa, except after going through the intermediate state 

 of a polyp. 



Or if we commence with the polyp, the series is thus : — 



1. The polyp produces bulbs that become Medusae. 



2. The Medusse produce eggs. 



3. The eggs produce polyps. 



This is what is called by Steenstrup " Alternation of Gene- 

 rations ;'' and he considers the earlier generation as preparing 

 the way for the latter. It certainly seems to be a most mys- 

 terious process : — a parent producing eggs which afford a 

 progeny of wholly different form (even so difi'erent, that 

 naturalists have arranged the progeny in another grand divi- 

 sion of the Radiata) ; and this progeny, afterwards, by a 

 species of budding or germination repeating the form of the 

 original parent. 



Yet although seemingly so mysterious, is not this mode of 

 development common in the vegetable kingdom \ Is it not 

 the prevalent process in the plants of our gardens, and fields, 

 with which we are all familiar ? 



It is well known to us, that in most plants, our trees and 

 shrubs for example, growth from the seed brings out a bud of 



