72 PHILOSOPHICAL TRANSACTIONS. • [ANNO 1790. 



The 3d objection, very far from being an urgent one, is, I am persuaded, a ca- 

 pital reason to believe that the seeming lateral internodia of the confervae, since 

 they are capable of cohering 2 or more together, and produce only 1 individual, are 

 true seeds, and not gems. The coherence of 2 living embryos, whether gems or 

 seeds, may form monsters, but it is equally impossible, in both cases, that perfect 

 individuals should regularly be formed by such coalition. Observation daily shows, 

 that of 1 or more neighbouring gems or seeds, 1 may thrive by rendering the other 

 abortive ; but, in this case, gems never cohere, the abortive one falls. In seeds, 

 on the contrary, not only the abortive coheres to the thriving one ; but this abor- 

 tion happens oftener in the several species of plants, in proportion as the seeds, by 

 their situation, are apt to cohere. In some genera it is even a regular proceeding 

 of nature, as in the dalea, lagcecia, hasselquistia, sapindus, ornitrophe, &c. These 

 objections having been I hope satisfactorily answered, I do not hesitate to consider 

 these grains of the submersed algae to be, what obviously they seem, their effective 

 seeds. The figure, formation, and temporary fall of these bodies, would never 

 have left any room for the above doubts, if their fecundation had been easily ac- 

 counted for. This point we must now proceed to investigate, and examine whether 

 the mucous substance which surrounds these seeds can be considered as true pollen. 



Pollen is by its nature immiscible with water, and specifically lighter than that 

 fluid. In the aquatic plants, which have a farinaceous pollen, the buds of the 

 flowers emerge from the surface of the water, and the fecundation is performed in 

 the open air. The phenomena attending the blossom of the potamogetones, my- 

 riophylla, vallisneria, &c. are too well known to require a particular mention. In 

 some aquatic plants, whose flowers have not the faculty of emerging from water in 

 the period of fructification, but still are endowed with farinaceous pollen, nature 

 has taken every precaution to defend it from that element. The flower of the 

 zostera is situated, and its fecundation happens, in the interior cavity of the stem, 

 which opens itself afterwards to let loose the fecundated seeds. The concave bases 

 of the leaves in the isoetes, closely adhering to each other, and perhaps more so in 

 the act of fecundation, forbid the entrance of water to the minute flowers situated 

 within them. In the pilularia, and marsilea, whose flowers are exposed to inunda- 

 tions, the fecundation is performed in perfectly closed vessels. Even in plants 

 living in the air, nature employs numberless well known contrivances, to shelter the 

 farinaceous pollen from the contact of water in rainy seasons. The pollen, to be 

 active in fecundation, needs not always be farinaceous. In most apocyneae it is ra- 

 ther a fluid ; in the orchideae it is an aggregate of solid parts, of a ceraceous ap- 

 pearance ; in some contortae it is found in a solid or rather viscous state. In the 

 pilularia, and marsilea, the particles of the pollen are kept in small bags of a mucous 

 substance, compared by Bernard de Jussieu to dissolved gum. The original state 

 in which it is found in every flower, before the act of fecundation, is that of a mu- 

 cus, but it is perfectly active even in that state, since its particles, after°becoming a 



