TU. | THE MECHANISMS OF FLOWERS. 383 
Orv. PRIMULACEZ. 
The species of Primula have been the subject of a series of 
_ interesting researches since Darwin first led the way. In his paper 
“On the two forms or dimorphic condition in the species of Primula, 
and on their remarkable sexual relations” (No. 154), he showed 
that in P. veris the stigmain the long-styled form possesses papilla 
_ three times as long as those of the short-styled form ; and that the 
jollen-grains of the long stamens are half as large again as those 
_ of the short ; that the same holds good of P. Awricula and P. sinensis ; 
j tl at these Primulas are very unproductive in absence of-insects,! 
but fully productive when artificially fertilised or when insects 
have access to them; and that in artificial fertilisation legitimate ® 
"crossings gave a yield half as great again as illegitimate. 
Hildebrand repeated Darwin’s experiments on P. sinensis, and 
ybtained almost identical results. He performed the additional 
experiment of fertilising flowers of each kind with their own pollen, 
nd found that this was the least productive of all ways. Also 
Hildebrand sowed the seeds which resulted from the various modes 
| f fertilisation, and showed that the union of two long-styled 
flowers produced mainly long-styled plants, and the union of two 
short-styled flowers produced mainly short-styled plants; while 
legitimate crossing of the two kinds of flowers produced offspring 
consisting of both forms in tolerably equal numbers (No. 340, 
1864). - 
_ Treviranus had already (No. 742, 1863), added P. farinosa, P. 
villosa, and P. minima to Darwin’s list of dimorphic species. Mr. 
John Scott (No. 692, 1864) enumerated altogether thirty-six 
‘species of Primula as dimorphic, and six as homomorphic, and 
showed that P. mollis was homomorphic and regularly self-fertilised, 
P. scotica homomorphic, but rarely self-fertilised, though fruit- 
ful to its own pollen, P. verticillata homomorphic, and usually 
unproductive when fertilised with its own pollen. 
| _ Axell figures the homomorphice and proterandrous flowers of 
P. stricta, and states that they fertilise themselves (17). 
_ Ricca describes P. longiflora, All., as homomorphic and proter- 
1 Darwin found that, in absence of insects, the long- styled form of P. sinensis 
twenty-four times as productive as the short-styled. Hildebrand found both 
je barren. 
i.e. the fertilisation of either —_ with pollen from the other form. 
