That the indusium is a special organ, i.e. not an eruption of the cuticle, I am sure; hence it is essential to examine extensively both indusiate and other forms, the precise extension of their veins, etc. at an early period to ascertain if their most diversified situations cannot be reduced to some one type.

Query.  Is the gyrate vernation of any ferns comparable to the form of certain shells, to which (at least Mollusca) ferns are supposed to be analogous.

Memo.  To ascertain the most peculiar, and most universal points of Mollusca and Pseudo cotyledonea, it is in this way that we may hope to extend our views.  Some there are indeed who, while the whole course of their studies has been to neglect structure, deny the applicability of presumptive evidence in favour of doctrines, the subjects of which are barely susceptible of direct proof.  Thus Greville and Arnott, angrily ask, what do persons mean by saying that mosses have pistilla, etc.? they protest against such community of application in the use of terms.  Many more deny sexuality because it has not been proved.  Considering the invisible nature of the fluid of the anthers of mosses, etc. how do they expect that we are to demonstrate its application to the pistil, and the subsequent steps?  As well might they doubt the necessity of the application of the boyau to an ovule, (or the existence of the boyau itself,) because the derivation of the embryo cannot be proved.

One word more; in all cases the appearance of the reproductive body after impregnation, is of late date; that date becomes later as we descend the scale.  The embryonary sac of Phaenogams does not always exist at the time of application of the boyau, and the appearance of the embryo is always posterior to this.

Again, ferns are superior to mosses in this, that in many cases the male influence is exerted directly on the parts that become the thecae, which is not the case in mosses.

18th.—­Continued examining ferns, and to-day completes my knowledge of the ramenta of three different genera.

In the first which is Cryptogamma, the resemblance of the young ramenta to the anthers of Jungermannia is evident enough, they are capital, and the head is at one period filled with granular matter:  so are the cells throughout, to a greater or less extent.  They are to be seen in all stages of development on the pinnae of a very young frond, those near its base having perhaps effected their purpose, while those at the apex of the pinna, or the prolonging part of pinnula, may be formed of only one cell.  It is curious that the terminal cell does not become spherical for some time:  in its earlier stages it is cylindrical like the rest.