APOGAMr. 



80 1 



require fertilisation, proceeding to form embryos without it, of which the highly- 

 developed Alga Chara criniia affords the only established (first by Alexander Braun) 

 example. This plant, which lives at the bottom of stagnant water, is met with 

 throughout the whole of North Europe exclusively as female individuals, which, how- 

 ever, and thus without fertilisation, yield abundant and normal germinating fruits. Male 

 plants of this species are known as isolated specimens from Transylvania, the south 

 of France, and the neighbourhood of the Caspian Sea, though their generative power 

 has not been investigated. It is evident that Chara crinita, like all other Charas, was 

 formerly sexually propagated, and that the power to give rise to progeny from the exist- 

 ing female apparatus even without fertilisation can only have appeared subsequently. 



To a second category belong three cases of Ferns, discovered and investi- 

 gated by De Bary himself and his pupil Farlow, which have long been known as 

 common garden plants, and possess the remarkable property of giving rise to new 

 Fern plants directly from the tissue 

 of the prothallium hy means of 

 simple budding. In two of these 

 Ferns (Pteris cretica and a garden- 

 variety of Asplenium. filix -femina- 

 cristaluni) no archegonia whatever 

 are developed on the prothallium, 

 although antheridia occur occasion- 

 ally. In Asplenium falcatum, on the 

 other hand, there are. found pro- 

 thallia completely devoid of sexual 

 organs and still capable of propa- 

 gation by means of budding, as well 

 as others with a few antheridia, and 

 finally prothallia which bear anthe- 

 ridia and archegonia, but neverthe- 

 less give rise to the Fern by simple 

 budding. There is still to be added 

 that in the three Ferns mentioned 

 this asexual propagation by budding 

 from the prothallium is the only mode, and that no example of them was found 

 with the embryo formed from an oosphere, whereas in very many other ferns 

 which De'Bary investigated with this object not a single one exhibited apogamy. 

 All the facts considered, there can be no doubt whatever even in the case of these 

 apogamous Ferns that the prothallia formerly gave rise to normal sexual organs and 

 propagated themselves in the ordinary way, and that Apogamy, the loss of sexuality, 

 was only, as physicians say, 'acquired' subsequently, and perhaps in this case 

 it depends upon the fact that the three Ferns in question have been cultivated plants 

 fof a long time. 



A point worthy of notice in the case of the Ferns just mentioned is that the leafy 

 shoot which really replaces the actual embryo, arises at that spot on the prothallium 

 where the archegonia would be formed in the normal case. In this respect the cases 

 of apogamy in some flowering-plants observed by Strasburger resemble them, 



[3] 3F 



FIG. 455. — Development of the adventitious embryos in Funkia 

 iwa/a (after Strasburffer X about 150). /apicalregionofnucellus of ovule 

 with the oosphere e and one of the synergidae s. II the cells shaded in 

 / have developed into the adventitious embryos a e, the oosphere re- 

 maining sterile. The tissue i belongs to the micropyle portion of the 

 integument. 



In 



