440 SCIENCE PROGRESS 



otherwise meaningless proportion 9 : 3 : 4 ; or perhaps we should 

 not say more than that the facts are consistent with the truth 

 of this theory. 



We will now pass from the culinary to the sweet pea, and 

 describe Bateson's beautiful experiment. One of the countless 

 varieties of the sweet pea grown to-day, Emily Henderson, a 

 pure white,' is remarkable for the fact that, whereas the pollen 

 grains of most other varieties are cylindrical with almost parallel 

 sides, some plants of it have this ordinary " long " pollen whilst 

 others have irregularly round pollen. The irregularity is never 

 so much pronounced that the round pollen can for a moment be 

 mistaken for the long. It may help those familiar with peas and 

 beans to say that the contour of the round pollen is never more 

 irregular than that of the most irregular wrinkled peas, whilst 

 that of the long pollen may be compared to a stout example of 

 the dwarf bean Non Plus Ultra. Bateson crossed the long- 

 pollened form of Emily Henderson with the short. The result 

 was a siveet pea of a deep purple colour. The purple of the 

 standard, the single outer erect petal, was of a redder shade than 

 that of the wings, the two petals just below the standard. This 

 sweet pea is known in the fancy as Purple Invincible, but is seen 

 more often now in cottage gardens than in up-to-date collections. 

 Its type of coloration is that of the original sweet pea as first 

 brought into cultivation. The wild Lathyrus odoratus — of the 

 Purple Invincible type — is common in Sicily. Here then is an 

 extraordinary case of reversion. Two pure white sweet peas 

 differing merely in the shape of their pollen are crossed, and 

 a hybrid with the coloration of the ancestor of all cultivated 

 sweet peas is the result. When these hybrids are allowed to 

 self-fertilise, there results in F2 a variety of forms already well 

 known to the fancy. These are : Purple Invincible again, 

 Picotee, Painted Lady, and Tinged White and pure whites. 

 Passing over the proportions in which the various coloured 

 forms appear, there are found to be 9 coloured to 7 white. 



Now, the 9:3:4 proportion in the culinary pea suggested 

 the existence of two pairs of characters, one of which — the purple 

 spot— could not be manifested in the absence of the other, the 

 grey coat ; though the grey coat could be manifested in the 

 absence of the purple spot. The 9 : 7 is accounted for by sup- 

 posing that colour in the sweet pea depends for its existence 

 upon the simultaneous presence of two factors of distinct 



