138 The Ottawa Naturalist. [Jan. 



permanently, and the strtictvires referred to are too insignificant 

 to be easily discerned in the rocks, if they have been preserved. 

 Moseley went so far as to say that were the foot-jaws only larger 

 they would, no doubt, occur in strata as old as the "Old Red 

 Sandstone." Phylogeny or the study of the pedigrees of animal 

 types, has available no generalized stem-form more interesting 

 than the Prototracheate Pcripaius. 



A NOTE ON THE COLOURS OF TUMBLING MUSTARD 



SEED. 



To those of us who have had to do with the seeds of Tumbling 

 Mustard (Sisymbrium altissemum) it is well known that these 

 are nearly always met with in mixtures of two distinct colours, 

 one kind being light-yellow, and the other dark-greenish. As a 

 rule the latter predominate to the extent of about three to one, 

 but occasionally the proportions are the other way about, while 

 still more rarely one colour may entirely dominate. Two or 

 more instances of the last condition were brought to my attention 

 during the winter of 1913, while I was with the Dominion Seed 

 Branch, at Ottawa. In these cases, samples of flax harvested 

 in Saskatchewan contained light coloured Tumbling Mustard 

 Seeds only, their purity being so tmusual that some doubt 

 was thrown upon the authenticity of the determination, thougthe 

 seeds did not differ in other respects. The only objection being, 

 therefore, that they were all of one colour instead of being mixed. 



During the autumn of 1914, my brother Stuart had occasion 

 to collect a quantity of Tumbling Mustard seed, and in doing 

 so visited a situation where the species had only recently become 

 established, probably not more than four or five years. By 

 that time, however, the plants had spread over a considerable 

 area and were sufficiently numerous to provide more than a pint 

 of seed. On examining the seed thus collected, it was at once 

 observed that all were of the light yellow variety, thus estab- 

 lishing the fact that they had evidently bred true to type, and 

 were therefore a distinct strain. 



This at once led to further investigation, and it was then 

 discovered that both colours were never met with together on 

 individual plants, but that one plant would produce only 

 yellow seeds and another only greenish . We have as yet found 

 no exception to this rule though plants of both types are fre- 

 quently met with growing side by side; in fact, they are seldom- 

 found otherwise, which would, of course, account for the two 

 kinds being nearly always mixed in samples of cultivated seeds. 



As the plants producing both kind of seeds areTgenerally 



