stout: pollinations in cichorium intybus 351 



is not reported. And it does not appear that tests similar to 

 those that LiUie has reported were made for the operation of any 

 auto-agglutinins or iso-agglutinins that would give some clue to 

 the intricate relation of self- and cross-sterility and fertility, and 

 for which such a hermaphrodite as Ciona seems especially favorable. 



Neither Darwin, Jost, nor Morgan (including his work of 19 10) 

 was fully aware of or took into consideration the fact that physio- 

 logical relations may operate to prevent cross-fertilization between 

 certain members of the same variety or strain (not involving the 

 so-called illegitimate pollinations in dimorphic or trimorphic 

 plants). That such may be the case is, from our present knowl- 

 edge, suggested by the results obtained by various early investi- 

 gators. Darwin ('68, pp. 169-170) states that it has long been 

 known that several species of Passiflora do not produce fruit 

 unless "fertilized by pollen taken from a distinct species." From 

 the evidence pertaining to Passiflora alata it seems highly probable 

 that certain cases of cross-incompatibility arose. In respect to 

 Gladiolus hybrids (pp. 172, 173), it is stated that "certain varieties 

 would not set seed although pollen was used from distinct plants 

 of the same variety, which had, of course, been propagated by 

 bulbs, but that they all seeded freely with pollen from any other 

 variety." Focke ('90 and '93) found that in Liliiini bulbiferum 

 all plants of the same clone were cross-sterile, but that sister 

 plants of seed origin were fully cross-fertile. 



In the production of fruit, especially in pears (Waite '95), 

 plums (Backhouse, '11), apples (Lewis and Vincent '09), and 

 cherries (Gardner '13), it has quite generally been known to 

 fruit-growers that certain varieties were "self-sterile," others 

 "partially self-sterile," and others "self- fertile." In the self- 

 sterile varieties . the self- and cross-fertility among plants of the 

 variety may be so feeble that the planting of other varieties as 

 pollinizers is often practiced. In these studies the horticulturists 

 have determined the more general facts that pertain to practical 

 results in fruit-growing. Aside from the fact that the propagation 

 of these varieties is vegetative the physiological requirements for 

 fruit development further complicate the processes of seed de- 

 velopment, but it is very evident that quite independent of these 

 factors a very marked physiological incompatibility is in evidence 

 in these varieties. 



