4GS PAUTllKNOOKNKSIS. 



8oen\s coiitrt\,ry to tlio oeououiy iil" plants tliat tlie i.\s>'j>'-oq11, pi-oduood at p'oftt oxpmw 

 uL" onoi-oy, muiI in ii souso tlio ouliuii\ntioii of a plant's aotivity, sliould witliw away 

 unprudiictivo. Plants with horniaphrodito flowtMvs can, if douiod orossing, i-osoi't 

 to autoo-niny. Hut this is of course impossible witli dioecious plaats; instsad of 

 autogamy the forinatinn of onibryos in unfertilizod oogonia and ovules is ii 

 possibility open to them, whoroby thoif outlay of material aixl energy shall not 

 bo wnstcnl. Ditpciovis plants, which i\w likewise annuals, two cspsoially liable 

 to the danj>'or of extinction in tlu^ absonoo of pollen a.nd consequent frult-pi-o- 

 duction; for thorn the death of the individual may connote tlie disappaarono© of 

 the spocios. Aji'ainst such possibilities ma.ny precautions oxist amongst pliuits, 

 notably tho formaiiii)n of ollshoots or brood-lK)dios; the leafy shoots arising from 

 those structures prosoi-\-o the plant fi'om suoli a contingency. In tl\o samo way 

 wo may regai'd the formation of brood-bodies in tlie ovules of dioeoious plants 

 as a moans contrived to prevent tho oxtinotion of the species. The fact tliat 

 brood-bodies aro formed in the ovuloa of not a. few dioioious plants to whidi 

 pollen has not roa,(ly access, supports this view. There has boon a speounsn 

 of the Californian bush, Obic/iie halimifolia (an Atriplm, Chenopodiaoeos), for 

 many years in the Vionna Botanic Garden. This plant is diosoious; tlio Vienna 

 plant boars only fomalo llowors, a,n(l pollen is not accessible within hundreds 

 of miles. Its stigmas remain unpollinated, aiiid its ovules unfertilized. But as 

 the autumn draws in, the ovarios of this plant begin to swell, and the porianth 

 which ensheaths the ovary expands, aind wha.t appear to be fruits aro formed, 

 But these fruits aro wliat wo call "deaf"; no signs of an embryo are to be found 

 within. Thus, in this plant, no brood-body has been produced; it is impossible 

 to say whether or no, at some former period, this plant ripened brood-bodies in 

 its Unfertilized ovules. Wliy the male plants of Ohara onnita are absent from 

 the Baltic, and those of Gnaphalium alpinum from the Arctic regions, are puzzles 

 as yet unanswered. In Ohara orinita it is only on tho coast-regions that male 

 plants are wanting; inland, male and female plants gi'ow side by side. Possibly, 

 climatic conditions and the vicissitudes to which our existing Flora has formerly 

 been subject have brought this about, but we lack the data for continuing the 

 discussion further. 



If, in the plants enumerated, parthenogenesis be but a special case of otllahooli 

 formation, it is a matter of indifference which cells within the ovule are the 

 starting-points for tho brood-bodies. In Ocelebogyne, in addition to the egg-oell, 

 other cells belonging to the wall of the embryo-sac are concerned in tho production 

 of brood-bodioB. Cells quite outside the ombryo-sao can also initiate these off- 

 shoots; in which case thoy project as little papilla) into the cavity of the embryo- 

 sac, whoro they continue their development. In this way several ombryoH may 

 arise side by side, a condition which has boon termed Polyembryowy, This phe- 

 nomenon occasionally takes place in the ovules of hoi'maphrodite flowers, in which 

 a normal pollination and passage of pollen-tubos to the mioropyle occur, This 

 is tho case in certain Liliaceio, polyeuibryony having been observed in species of 



