184 I-Hh : OUTLINES OF GENERAL BIOLOGY 



Parasitism among plants is even more diverse in its forms and 

 gradations than among animals; and its variety brings home to us 

 the idea that degeneration is not always the nemesis of becoming 

 tlt'j)endrnt on another organism for sustenance. No one can call a 

 {>artial jKirasite like the mistletoe a degenerate plant, yet it is 

 entirely dejx'ndent on its host. Even in regard to easels like dodder, 

 where the leaves have gone, there is consideral)le floral exuberance, 

 prothicetl it is true at another's exjxMise. In an extreme case like 

 Kaftlesia. sans leaves, sans stem, sans roots, we must give the plant 

 credit for a sujHTlative flower. In many parasitic plants there is 

 marked reduction of parts, but against that there has to be reckoned 

 the development of sjHcial adaptations, such as haustoria. 



There is another point, that we be careful not to put the cart 

 iK'fore the horse in interpreting the reduction of parts and qualities 

 in some parasitic plants. For the Ivginning of reduction and weak- 

 ness may Ix* seen in some plants that are in no way parasitic, and 

 such a reduction might make an incipiently parasitic mode of life 

 highly advantageous. Thus, as Skene points out, golden-leaved 

 varieties are not uncommon among cultivated plants, and indicate 

 a deficiency of clilorophyll which would be fatal in natural condi- 

 tions, unless indeed the plant took or had begun to take to, say, 

 root -parasitism. We have referred to the yellowish colour of Tozzia, 

 the Alpine relative of our eyebright, and "we may look on Tozzia 

 as the ftrst step in the process of reduction". 



We mean that some weakness, such as chlorophyll-deficiency or 

 leaf-reduction, may be a precondition of parasitism. That is to say, 

 if opi)ortunity is offered to these incipiently weakly plants — and 

 op|H)rtunities of rcKU-parasitism seem to be frequent — a variation 

 in the direction of parasitism may have immediate survival value. 

 Is not reduction as likely to be the cause of parasitism as parasitism 

 of reduction;' 



ECOLOGY OF PLANT REPRODUCTION 



The merely outline survey here attempted has to do with the 

 Natural History of repro<luction in plants, and in particular with 

 }x)l]ination and seed-dis|xTsal. 



There are four main nuKles of mult ijilicat ion in the plant world. 



(r/) The simplest of all is seen when a unicellular Alga or fungus 

 divides into two units which then go apart. Not far removed from 

 \h\^ is the budding of a miireliular organism such as a yeast-plant, 

 or the rapid division within the cell wall or a s]x?cial cyst, the result 

 In-ing to form "s|x)re-cells" which have the advantage of being 

 motile in some cases, or of Ining very resistant (to drought, etc.) 

 in other cases. 



