FERTILIZATIOy IN PLANTS ' 221 



The nature and origin of the achromatic elements involved in the 

 fertilization of plants is still almost wholly in the dark. No observer 

 has yet succeeded in observing either centrosomes or asters in the 

 fertilization of the thallophytes, despite the fact that in some of these 

 forms mitosis takes place with both these structures in a manner 

 nearly analogous to that observed in animals.^ In the cycads Zainia 

 and Cycas, Webber and Ikeno ('98) agree that the entire spermato- 

 zoid enters, but only the nucleus appears to be concerned in fertiliza- 

 tion. The cilia-bearing band — a product of the blepharoplast, and, 

 as described at page 175, probably the analogue of the middle-piece 

 of the animal spermatozoon — remains near the egg-periphery, gives 

 rise to no astral or other fibrillar formations, and apparently remains 

 quite passive (Fig. 108). 



In angiosperms, too, the evidence seems to show that no centro- 

 somes are concerned in fertilization. Guignard ('91, i ), in a very 

 detailed and clearly illustrated paper, gave an account of the centro- 

 somes in the lily agreeing almost exactly with the " quadrille of 

 centres " as described by Fol,^ paternal and maternal centrosomes 

 conjugating two by two. The later and very careful studies of Mot- 

 tier and others have, however, entirely failed to confirm Guignard's 

 results, the germ-nuclei fusing without the participation of centro- 

 somes or astral formations, and after a time dividing, without centro- 

 somes, in the manner characteristic of the higher plants.'^ Neither 

 in the cryptogams has any one thus far succeeded in finding fertiliza- 

 tion-centrosomes or asters at the time the germ-nuclei unite. Stras- 

 burger contributes, however, the interesting observation that in Fuciis 

 the cleavage-centrosomes afterward appear on that side of the 

 cleavage-nucleus derived from the sperm-nucleus, which he believes 

 from analogy may indicate the importation of a " new dynamic 

 centre " into the egg by the spermatozoid.^ Combining these facts 

 with the phenomena involved in the origin of the spermatozoids, 

 Strasburger suggests that the sperm-nucleus may import into the 

 egg either a formed centrosome (probably thus in Fucns) or a cer- 

 tain quantity of " kinoplasm," which incites the mitotic phenomena 

 in the absence of individualized centrosomes.^ This view harino- 

 nizes with that suggested at pages 1 1 1 and 214, and we may perhaps 

 here in the end find a reconciliation between the various types, not 

 only of fertilization but also of mitosis, in plants and animals. 



On their face the facts of fertilization in plants, especially in the 

 phanerogams, seem to indicate that the stimulus to development 

 is given by the paternal germ-nucleus. Nevertheless, the analogy of 

 animal fertilization would lead us to expect that the fertilizing sub- 



1 Cf. p. 82. 3 Cf. p. 82. ■ 5 'gy^ p. 420. 



2 Cf. p. 210. * '97, p- 418. 



