614 THE SUBDIVISIONS OF THE VEGETABLE KINGDOM. 



are those of Diatoms, whose cell-wall is transformed into an imperishable siliceous 

 frustule, together with those Florideffi which provide themselves like corals with a 

 calcareous skeleton, and some tough Sea-wracks. It is, however, a very significant 

 fact that the innumerable fossil Diatoms which come to us in so-called tripoli-powder 

 and Diatom-earth, and the many calcareous Floridese which come down to us as 

 Xullipore banks are deceptively like those living at the present day, that these 

 groups have remained unaltered for eons, and that no form has been discovered in 

 any of the older strata which could be regarded as a link with another group. No 

 fossil remains are known beyond doubt to exist of the numerous aquatic plants 

 with delicate cell-walls which perish as rapidly as they develop, of the SpJaerella 

 species wiiieh give a red colour to rain-water and to the snow-field, of the micro- 

 scopic Desmids, of the green filaments of Spirogyra, of the remarkable green tubes 

 of Vaucheria pictured in plate I., &c. Some woody Polyporus species of Fungi have 

 reached us, but in forms which look very like those at present growing on old 

 tree-trunks. Some species of Moulds have been preserved in amber. I have before 

 me a piece of amber in which insects are imbedded; from one of them spreads a 

 web of mycelial threads which doubtless belonged to some mould-like Fungus such 

 as to-day attacks various insects. The myceliums of various Fungi, also, are found 

 penetrating the tissues of many of the fossil cryptogamic stems of the Coal Measures. 

 This fact is very instructive, since it shows that in the tertiary period, and in much 

 earlier periods also, the relation of saprophytic plants to the dead bodies of 

 animals and plants were the same as they are to-day. All these results taken 

 together prove that delicate Thallophytes whose cells do not become siliceous or cal- 

 careous, or which are not inclosed in resin, cannot be preserved in a fossil condition. 

 But no one would conclude from this that the groups to which such delicate 

 growths belong were not represented in earlier periods. 



On comparing the past and present of the Vegetable Kingdom from these points 

 of view, more especiallj' with regard to the question whether existing groups 

 stood side by side in earlier periods also, or whether, in the course of time, they 

 have sprung from a single individual or from a few spontaneously-generated indi- 

 viduals, we are obliged to decide in favour of the former. The so-called " higher " 

 plants are not derived from the so-called " lower "; the groups of higher and lower 

 plants co-existed from the beginning side by side. But variations within the limits 

 of each group have alwaj^s taken place. New species, i.e. new groups of species, 

 arose in consequence of the crossing of the species already in existence. Of these 

 the species which were best suited to the climatic conditions of the time being 

 survived. But the variation in the formation of new species never went so far as 

 to do away with the characteristics of the group. We immediately recognize in 

 the fossil Laurel-trees, Magnolias, Oaks, Palms, Grasses, Pines, Equisetums, Ferns, 

 Lycopods, Floridete, Diatoms, and Moulds the ancestors of the now existing species. 

 This would be impossible if the group-characteristics had disappeared in the modifi- 

 cations which the species have undergone. 



When I now attempt the task of stating in detail what has been furnished by 



