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propagulmn. This view has been adopted by Agardh, and 

 may be considered the notion commonly held by botanists. 



" The opposite and older opinion is still held and defended 

 by Aresehoug, an able Swedish algologist, and, in this country, 

 by Mr. Thwaites, of Bristol, a most expert and accomplished 

 cryptogamic botanist, and a distinguished physiologist. These 

 authors consider that as the spores are usually formed in special 

 organsorcowce/)iac/e5, accompanied by peculiar transformations 

 and the growth of special tissues, and as the tetraspores are 

 commonly dispersed through the substance of unmetamor- 

 phosed branches, i\ie former have more the character of special 

 reproductive bodies than the latter, and should therefore be 

 regarded as the representatives of seeds. This reasoning will 

 apply to a considerable number of cases, but not to all, for in 

 many instances we find tetraspores formed in special organs, 

 as complex in structure as the conceptacles of the spores. 



" As far as 1 am concerned, I have hitherto hesitated to form 

 or express any opinion on this puzzling matter, believing that 

 the evidence was pretty nearly balanced, and that deductions 

 which appear clear when we take in only a few selected cases 

 are considerably weakened when the whole subject comes un- 

 der review. I could never quite give up the seminal nature of 

 the spore, yet, in many cases, I was forced to admit the high 

 organization of the tetraspore. And there are cases in which 

 it is diflBcult to say whether the body be a spore or a tetraspore. 

 One of these anomalies occurs mCorallina, in which genus we 

 have quadripartite spores (or tetraspores) contained in concep- 

 tacles. These bodies are, by tlieir position, strictly analogous 

 to the spores of Polysiphonia, and yet in their structure they 

 have the character of tetraspores. Cases of this kind, and they 

 are by no means isolated, make me very cautious of expressing 

 a decided opinion at present on this question. Meanwhile 

 some arguments, resting partly on analogy, partly on observa- 

 tion, have recently suggested themselves to me in favour of 



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