136 Darwin on the Effects of Cross- and Self ■ Fertilization. 



the other) is so prevalent that it may almost be regarded as the 

 rule ; and this ensures such crossing between few-flowered 

 plants, and greatly favors it in the case of spikes, racemes, and 

 the like. For, proterandry being the commonest arrangement, 

 so that the younger flowers act as male, and the older as female, 

 and bees habitually alighting at the bottom and proceeding 

 upward, they carry the pollen from the upper and younger 

 flowers to stigmas of the lower and older flowers of the next 

 spike, and so on. Heterogonism (see this Journal for Decem- 

 ber, p. 82), which is less commoi v like com- 

 plete dioecious separation of the sexes in this respect, and with 

 the advantage that all the individuals arc seed-bearing. Most 

 of the special arrangements peculiar to certain families, such as 

 Orchids, or to plants — such as Posoqueria, with its woadreui 

 mechanism for quickly stopping "out access to the stigma when 

 the pollen is violently discharged upon some insect, but opening 

 the orifice the next day — are of a kind to favor the crossing of 

 distinct plants. Piepotency of other pollen, which may accom- 

 pany the other arrangements or exist independently, acts largely 

 and powerfully toward the same end. Our author investigates 

 this at some length : we cite for illustration a single but a strong 

 case. The stigmas of a long-styled Cowslip were supplied with 

 pollen from the same plant, and again, after twenty-four hours, 

 with pollen of a short-styled, dark-red Polyanthus, a variety of 

 the same species:, from the resulting seeds twenty seedlings 

 were raised, and all of them bore reddish flowers ; so that the 

 effect of the plant's own pollen, though placed on the stigmas 

 twenty-four hours previously, was destroyed by that of the red 

 variety. The same thing is shown by the impossibility i}\ 

 many cases of raising two varieties of the same species pure if 

 they grow near each other. " No one who has had any experi- 

 ence would expect to obtain pure cabbage-seed, for ine 

 a plant of another variety grew within 200 or 300 yards." 

 And a veteran cultivator once had his whole stock of seeds 

 seriously bastardized by some plants of purple Kale which 

 flowered in a cottager's garden half a mile away. Mr. Gordon 

 records a case of the crossing between Primroses and Cowslips 

 through pollen carried by bees over more than two kilometers, 

 or an English mile and a quarter. 



We must copy the close of this section — long though it be — 

 because of ;>n of the topic in hand, and for 



the teleological lesson which it teaches. 



"The case of a great tree covered with innumerable hermaph- 

 rodite flowers, seems at first sight strongly opposed to the be- 

 lief in the frequency of intercrosses between 

 The flowers which grow on the opposite sides of such a tree will 

 have been exposed to somewhat different conditions, and a cross 



