September 1, 1898.] 



KNOWLEDGE. 



213 



will escape into the surrounding water, and shortly each 

 will be seen to take the form of a spirally coiled sperma- 

 to/.oid with a more or less defined disc at one end and a 

 tuft of cilia at the other. 



It thus becomes evident that these little bodies, which can 

 be found in any greenhouse round growing ferns, though 

 not so easy to distinguish out of doors, are true egg- 

 bearing plants. They are, in fact, the real oGphyte statje 

 in the fem-plant's life-history, and we are forced to the 

 conclusion that we must look on them as the equivalent 

 of the moss-plant with its stem and leaves, and re,t,'ard 

 the familiar fern as the representative only of the stalked 

 capsule or sporophyte of Mnium and ■lumjcrnuinnia. 



The two generations have, as it were, changed places in 

 respect of size, conspicuousness, and elaboration of 

 structure. 



While it is impossible to exaggerate the importance of 

 this " alternation " in the life-history, it remains difficult 

 to decide whether we should regard the two stages as 

 fundamentally different, or look on them as extreme 

 specializations on distinct lines of a type with double 

 potentiaUty. Thus, we cannot overlook the facts that in 

 a few exceptional cases the formation of Archegonia can 

 be dispensed with, and the prothallus may grow out 

 vegetatively into a sporophyte (" Apiy/min/") ; while, on 

 the other hand, the tissues of a frond may, in rare cases, 

 develop prothalli without the intervention of spores 

 {" Apospory "). 



We have, in fact, crossed a wide gap in the continuity 

 of vegetable Ufe. We have passed from a type in which 

 the sporophyte grows from, and is physiologically dependent 

 on, the parent egg-bearing plant, to one in which the 

 oophyte generation is small, inconspicuous, transitory, and 

 of simple structure. The sporophyte has become a highly 

 specialized growth, with complicated systems of tissues 

 like those of flowering plants ; ranging through an 

 infinite variety of forms, from the moss-like fronds of the 

 filmy ferns to the rigid tree trunks of the Cyatheas and 

 Alsophilas of the Tropics. 



With the detailed structure of this sporophyte we are 

 not here concerned ; but to complete our summary of the 

 life-history the cycle of reproduction may be summarized 

 as follows : — 



Division of the fertilized egg-cell produces a fern-embryo 

 which develops a primary root, leaf, and stem growing- 

 point long before the final decay of the Oophyte or 

 Prothallus. When the latter has dried up and disappeared 

 the stem of the fern-sporophyte is in active growth ; 

 producing successive leaves or fronds behind the pro- 

 gressive apex, and establishing firm connection with the 

 soil by its numerous roots. The fronds from the first 

 perform all the functions of leaves in the vital economy of 

 the organism, and in their older stages take their part in 

 the reproductive cycle by developing Sporangia. These, 

 in the case of the true ferns, are formed each from an 

 epidermal cell, though as numbers of such cells are active 

 together the result is usually 'a group or Sonisot sporangia. 

 The form of the sporangium varies, and special forms 

 characterize particular groups, but in all our common ferns 

 the type is that shown in the figure. The position and 

 shape of the suri, and the form of their membranous 

 covering or indusium when present are characters of great 

 importance to the systematic botanist. Through the 

 whole series of true ferns, however, whatever their variety 

 of appearance, the spores are of one kiwi onh/, and when 

 they germinate produce a free green prothallus such as we 

 have observed. 



Having thus got some idea of the life-history of a fern, 

 it only remains to see if we can get any glimpse from this 



standpoint, either backward or forward, along the lines of 

 plant evolution. 



Looking downward, it is very remarkable that we can 

 see no evident links connecting the fern-type and the 

 moss-type. It is possible to imagine a moss in which 

 leaves mif;ht be formed on the seta, or in which the 

 sporophyte might root itself and live after the oophyte 

 had perished, but as a matter of fact we do not know of any 

 such types. It is also possible to imagine a moss-capsule 

 becoming complicated in structure by internal division into 

 chambers, owing to certain cell layers not forming spores; 

 and later by the separation of these layers so that the whole 

 sporophore became a compound structure. Prof. Bower has 

 shown how the various types of "fructification" in the 

 vascular cryptogams may in this way be compared with 

 one another, and with some relatively simple ancestral 

 type. It is, of course, neither necessary nor reasonable to 

 suppose the fern derived from a specialized moss-type, but 

 it is probable that the whole series of the vascular crypto- 

 gams — ferns and their relatives — might, if the intermediate 

 links were still existing, be traced back to some form 

 having relationship with both mosses and liverworts. 



Looking in the other direction, the question arises, what 

 is likely to be the next stage in the series if the subordina- 

 tion of the Oiiphyte generation continues ? It wUl be some 

 plant in which the prothallus is still smaller, more 

 ephemeral, and less independent. In our next study we 

 may find that this link in the chain between the lower 

 and higher plants is also easily obtainable, and almost 

 equally easy to observe. 



NOTES ON COMETS AND METEORS. 



By W. F. Denning, f.b.a.s. 



Comets. — Though we have recently had a numerous display 

 of comets they do not seem to have furnished any special 

 instance of brilliancy or peculiarity of appearance. The 

 positions of the objects referred to are, in the majority of 

 cases, unfavourable. Perrine's comet of March 19th is 

 now exceedingly faint, and during September will be 

 almost stationary in about R.A. 6h. 32m. Dec. fifty- 

 one degrees north. The comets of Coddmgton, Encke, 

 and Perrine (June 14th) are too far south to be favourably 

 seen. Giacobini's comet is becoming very faint. Wolf's 

 periodical comet, is still visible in the morning hours, 

 but it requires a good telescope to show it, as it is by 

 no means a conspicuous object. The following is an 

 ephemeris by Thraen for Berlin mean midnight : — 



Comet Wolf. 



Distance in 

 Date. R.A. Declination, millions of 



1898. h. m. s. o ; mjgg_ 



September 11 G 6 7 +9 31-8 153 

 1.5 6 13 38 +8 24-2 151 

 19 6 20 45 +7 14-2 150 

 23 6 27 26 4-6 22 148 

 27 6 33 41 +4 48-4 147 

 During September its brightness remains practically 

 constant at 2-6. From the ephemeris it will be seen that 

 the comet moves slowly to south-east passing from the 

 north-easterly limits of Orion into the head of Monoceros. 

 On September 23rd the comet will be in conjunction with 

 the 6th mag. star 12 Monocerotis, and about one and 

 a-quarter degrees north of the star. 



Meteors.— Fireball of July I4.th. — A brilliant fireball, 

 apparently as large as the moon, was seen on July 14th at 

 9h. 50m. by Mr. Murrell Dawnay from a position about 

 two miles off Beachy Head. The path of the fireball 



