48 



the surface of the axis dark, and polished. Ellis has made 

 observations similar to these on this genus*, which have not 

 heen allowed to have their dne influence in the formation of 

 the theories of some of our physiolojiists. 



The axis is solid, horny, fibrous, flexible and formed by a 

 series of concentric layers. It varies in thickness according 

 to age, and is more solid in the older portions than in the 

 branches which are of a horny membranaceous texture. 

 Though the thickness of the axis is in accordance with th^^ 

 age of the specimen, yet it depends for its existence on the 

 soundness of the fleshy crust. For if from accident or the 

 incrustation of corallines, the axis be denuded, it ceases to 

 increase, while above and below the point of denudation it 

 grows as usual. In a transverse section the concentric 

 layers, in lighter and darker lines, are very observable, with 

 the while central pith. This view bears a great resemblance 

 to a similar section of the wood of an exogenous plant, but 

 presents two remarkable deficiencies in the absence of the 

 radiating medullary rays and cells which render the wood 

 such a beautiful object for the microscope. The axis near 

 the root is very compact and the circular layers consequently 

 less distinct than higher uj> ; in the branches it is merely 

 membranaceous. In a longitudinal section the concentric 

 layers are as apparent as in the transverse one and it 

 very closely resembles a similar section in wood. It is 

 fibrous and rends very freely. In different parts of this 

 section white spots of a cellular substance are frequently 

 observed irregularly distributed between the horny layers. 

 This is most frequently observed about the root in the 

 axillae of branches, especially where t«o arise close to 

 each other. In such a case I have frequently seen several 

 successive layers of it with a few of the horny fibres be- 

 tween, and in a case now before me there are five very 

 distinctly marked. The white substance, mentioned before 

 as being found in the large cavities of the branches, so closely 

 resembles these white spots in colour and texture as to point 

 to a common origin for their production : a secretion or for- 

 mation from the investing membrane. This appears to be the 

 substance, supposed by Ellis to be the remains of a portion 

 of the fleshy crust which had been enclosed between the 

 horny layers. He says, '' we frequently meet with layers of 

 calcareous matter enclosed between the circles, which is 

 evidently nothing else but the decayed flesh of the animal, 

 which has been covered and enclosed by the subsequent 

 growth of the san)e aniujal." This however, I believe is not 

 the true explanation ; in the case of the globular excrescences 



• Ellis and Solander's Zooph., p. C9. 



