742 



LECTURE XLI. 



of a block of turf saturated with nutritive substances. The result is that in the 

 course of several weeks tiny plantlets are produced, usually in dense tufts, w-hich 

 on closer investigation are seen to be of two kinds, namely, smaller male plants as in 

 Fig. 42^ A, and much larger female plants as in Fig. 426. Consideration of the 

 figures referred to shows that the plantlets produced from the spores (which moreover 

 are very difficult to cultivate) present not the slightest similarity to an Equisetum 

 plant. The latter is in every respect a highly organised plant, its roots accord 

 entirely with the type of the higher plants, its shoot-axes and leaves are clothed 

 with a very strongly developed epidermis, and the fundamental tissue of the shoot- 

 axes contains strands of sclerenchyma, in addition to colourless and green paren- 

 chyma, and the vascular bundles, although thin and delicate, nevertheless possess 

 all the essential elements of such. Matters are quite otherwise with the plantlet 

 produced from the spore, the branched shoot of which possesses assimilating 

 chlorophyll, it is true, but in other respects presents the simplest cellular structure ; 

 the roots are simple long utricles. 



It is already clear that the germination of the spore of a Horse-tail signifies 

 something very different from the germination of a seed of the flowering plants ; 

 even the tiniest seed, such as that of Tobacco or of a Campanula, contains a young 

 plant, an embryo, which on its first development at once reproduces the characters 

 of its mother-plant. It would therefore be very inappropriate to name the small 

 plantlets developed from the spores of the Equisetum simply embryos, since they play 

 an entirely different part in the developmental history ; they are usually termed 

 prothallia. 



The small male prothallia of Equisetum give rise at their margins to several 

 antheridia which form only a few antherozoids. They consist of a simple layer of 

 cells and a core of tissue each cell of which produces one antherozoid. The ap- 

 pearance of the latter is shown in Fig. 425 -5 and D ; like those of the Ferns the 

 antherozoids of the Equiseteae have also numerous cilia for the purpose of executing 

 swimming movements, since as in the case of the Algae and Mosses, and as in all 

 Vascular Cryptogams, fertilisation by means of antherozoids can only take place with 

 the aid of water, even though the prothallia grow on soil which is only damp, 

 where the sexual organs become so far ripe that on the opportune saturation of 

 the whole tuft with water the antheridia and archegonia open, and the antherozoids 

 can swim from the former to the latter. 



The archegonia of the female prothallia are represented in Fig. 426 at a. 

 They have in the main the same structure as those of the Moss, only they are 

 more simply organised and their ventral portion is immersed in the tissue of the 

 prothallium, from which only the neck protrudes. Here also the oosphere arises in 

 the venter of the archegonium as a rounded mass of protoplasm lying free in the 

 central cavity. Here also an open canal leads to the exterior from which the 

 deliquescent canal-cells are expelled at the moment of opening. I am not 

 aware that any one has as yet observed the entrance of an antherozoid into the 

 oosphere itself, in Equisetum; but that this occurs there can be no doubt, since 

 in the case of the Ferns and their allies various good observers have repeatedly 

 succeeded in directly observing the act of fertilisation. 



After fertilisation the canal, as in all archegonia, becomes closed. The oosphere. 



