RECREATITE SCIENCE. 



157 



The little " Ulva crispa," gathered last, is 

 always a favourite object (Fig. 3) with its 

 bright green endochrome dotted with a charm- 

 ingly regular irregularity over the delicately 

 transparent membrane of the frond. With 

 the mature plant may often be found narrow 

 flat threads as at h, which show in an instruc- 

 tive manner how a broad leaf-like expansion 

 may be formed by repeated cell-divisions, 

 now in a longitudinal direction and then in a 

 transverse direction. Some of the pretty 

 bright green cell-contents have escaped, and 

 taken on an active animal-like existence, as 

 at d. The specimen from which our figure 

 was taken swarmed with them, and though 

 we did not actually witness any of them 

 escaping, such has been seen. Numerous 

 Euglenae (Fig. 4) occurred with them, of 



Fio. 4. — a, motile ; and 6, resting condition of 

 Euglense. 



which all that can be said here is simply to 

 stimulate inquiry ; though so thoroughly 

 animal-like in their movements, altering their 

 shape continually as they move over the 

 field, vibrating the little whip-like cilium or 

 two vrith which they are furnished — with 

 their little red eye-like speck, and at some 

 stages of their existence a small vesicle dilat- 

 ing and contracting at intervals heart-like, 

 yet these are now known to be only motile 

 spores (the name given to bodies analogous to 

 seeds produced by non-flowering plants). The 

 stages of growth of Ulva are not yet fully 

 known, and it seems possible that the Eu- 

 glense forms found on this occasion with the 

 Ulva might be motile spores of the latter. 

 Having sought to attract to the study of 

 these humble plants, by showing how elegant 

 their appearance is under the microscope. 



how instructive the little we yet know about 

 them, and how much of yet greater interest 

 remains to be learnt of the history of their 

 life, let us briefly glance at the important 

 part borne by them in the economy of Na- 

 ture. In poesy, the intensified and spiri- 

 tualized reflection of the popular mind, mis- 

 taking the cause, it is held that they are per- 

 nicious in their effects. 



" Mantled o'er with green, 

 The stagnant pool,' " 



is a familiar representation of all that is foetid 

 and unwholesome. But is it indeed owing 

 to this green vegetation that such is the case ? 

 Nay, on the contrary, the very opposite is 

 the fact. Is there such a collection of foiil- 

 ness ? Borne on the four winds of heaven, at 

 once the Oscillatoria and allied types of vege- 

 tation appear to commence their mission of 

 usefulness to man. Look at the portion left 

 in the watch-glass : the spot where it was 

 crowded together, a shapeless, unsightly sub- 

 stance, is now deserted, and instead, it has 

 wormed its way to the extreme edges of this 

 miniature collection of water, the ends all 

 pointing outwards, as they would go further 

 " 'an if they could." Even to the naked eye, it 

 is now a pretty spectacle, the threads forming 

 a delicate green fringe round the margin of 

 the glass. Thus, in the pools they spread, 

 increasing with amazing rapidity, feeding on 

 agencies destructive to our hfe, oxygenating 

 the water, and through it the air in the 

 neighbourhood of which they grow. By 

 their decay a soil is formed for plants of a 

 higher type and with higher powers of use- 

 fulness. But let us, especially the dwellers in 

 great cities, forget not how much we owe to 

 the unthought of agencies of " that green 

 stuff;" in revivifying the "used-up" atmo- 

 sphere we are compelled by the circumstances 

 of position to breathe, and let us not again 

 attribute to them, our friends, ill effects 

 which they are incessantly doing their ut- 

 most to counteract. 



TUFFEN WbST. 



