CHALAZOGAMIC FKKTIUZATION. 



413 



not 80 dinet. Here it passes by the emljryo-sac on one side and then turns sharply 

 do\m agsui> reaching the e^-cell from the same direction as it would have done 

 had it entered by the micropyle (cf. %. 314 b, p,t). It is interesting to note that 

 in iMny nearly aUied Amentacesa, as in the Cupnliferse, which includes the Oak 

 (QiwrvMsX Beech (Foffws), and Chestnut (Ctu^fnurtitV fertilization is by the micropyla 

 The following table indicates the method of fertilization as at present known in 

 the varioas families comprehended in the group 



CSMliiingxiluc 

 Not ascettained. 



AXBSTACEJB. 



I. 



Bettda ) 

 Jimms ) 



Hornbeam (CfanpuMK) ) 

 Hop Hornbeam {(ktrga) 



3. Goqpulifaraa. 



Otik{QH«rmis) 



Ghcstaut {Oa^a»ea) 



4. Jv^andaeete. 



Wafamt (.^i^fems) ... 

 Goya, Ptsro-enrjrEr, &e. 



3. Mvikaeeee^ 



Sveet Gale {Jfyriea) 



5. CtsasaiBeai 



CbsHartNo... 



7. Salkanesew 



TTillo^ (SaUx) I 



J 



.. Porc^amic. 



.. Boarogamia 



... >Cot asoeitMiied. 



... Forogamic 



... Oiaiaxogamic. 



... Fwogamic 



1%. SU B. — CtalxHisaanie &itili»tion in Oie 

 Alder (Abni«9J«(u«n«). Kasruunntie. 



Itie ctnvii^ diovs one half ti a loi^tndinal 

 section «f Ok omy. Hie wall ot the oraiy 

 fe tliiek, and Ins a harloied middle ]aj«r 

 (shaded daita A! thelopis thel>ase«*iaie 

 style, ft»m irhich the pciUea-tnbe lj»-t) tan 

 be tiaced pi^i^ straight on Ihroush the 

 snletauce ot the oTaij- to the OTUle. Xntio^ 

 ins the OToIe bf its point ot attachment n> 

 fl>e placenta the pcOlot-tnbe bends shaif^ 

 npvaids (at the ehalaxa) into the nneeUiK. 

 It now pass^ br ti>e small oval embi3«-sac 

 on the inn^ side, and «h@a below the micrtk- 

 p^e tains shaipljr down to the apex oi fl>e 

 ^nbij'O-sae. Ibe Tascular supply (^ tiie 

 OTides. which foniK a colamn In the idaeat- 

 ta, is shaded dait OiHeidaahljr odaised 

 Qtom a drawins b; 31. F. £waitX 



have been made fnmi 

 to time wii^ a view to explaining the 

 phmomena attendant on the wandering of the 

 polka4abe from l^e sl%ma to the micropyle. It 

 has hesDi shown tliat the poUen-tabe is extremely 

 ssosative to various estemal oonditions, and that 

 by aq^coptiately varying these tiie diredion 



followed by the tube in its growth may be controlled. Pollen-tubes are espedaJly 

 sanative towards sogar^solutions, and bend out of tieir cotuse towards the sugar. 

 Hsey also tend to grow away from the air, and show a preference for spaces satu- 

 rated with aqneoos vapour to such as are less humid. Of aU the conditions which 

 •feet a poUen-tnbe, m«Kt conspicuous is tiie attraction which sugar exerts upon it. 

 Vwaous porticms of tiie pstil exert a dmilar chemical stimulus on pollen-tubes, very 

 n»A^ bang the action of the micropyle in this inspect. A few of the experiments 

 *Bwwstrating this attractive prv>perty of stigma and ovules may be briefly 

 dssaihed. If a fresh mature stigma be cut off and laid on a plate of gelatine, and 



