58 NATURE-STUDY REVIEW [11:2— Feb., 1915 



never produce seeds the students were set to examine the flowers 

 of both kinds and to compare the number and arrangement of their 

 floral parts and so, mayhap, to discover the cause of the sterility 

 of the double flowers. In the latter neither anthers or pistils 

 were found, — certainly no anthers. Then came the practical 

 application in the attempt to answer the question — How may we 

 from the material here, secure double flowering plants for next 

 year's garden? The roots were examined to see whether root- 

 division offered the answer. The class reached the conclusion 

 that slipping would have to be resorted to ; accordingly some slips 

 were selected for trial. The teacher invited speculation as to how 

 the first double flower may have been obtained and worked with 

 the suggestion that it must have come accidentally — ^"a sport." 

 What has happened once might happen again so it might be worth 

 while to experiment with some of the single-flower seeds. Two 

 of Burbank's successes in this direction were mentioned. 



(2) Flower-aggregations were quickly discovered in examples of 

 sweet alyssum, verbena, shepherd's purse and candy-tuft. Speci- 

 mens of the inflorescence were taken to the class-room for compari- 

 son with each other and with the cornflower (Centaurea) . 



(3) The door-yard knot-weed or "goose-grass" was found and 

 observed not only on the almost bare path but also on the grassy 

 path and among grass quite off the pathway. Where are the 

 plants most vigorous ^ The longest stems were on the last named 

 situation but the most vigorous plants along the grassy paths 

 and in patches considerably trodden. Why there? The theory 

 offered that in wet weather the seed is distributed by the travel- 

 ler's feet accounted for the presence of the plants but not for 

 their comparative vigor in the different situations. The pressure 

 of the heel on their stems and on the leaves of dandelions and the 

 leaves and stems of some other plants afforded means of comparing 

 injuries by treading. The stems of the knot-weed were injured 

 only on the path or ground where it was bare and hard and even 

 there the small leaves escaped. But why are the plants less vigor- 

 ous when they are scarcely or not at all trodden? Comparison with 

 the dandelion on the spot was invited whose rosette of radical 

 leaves smothers out competitors. It was at last concluded that 

 where there was just enough treading to keep down the grass and 

 other softer plants the door-weed would receive more light and 

 air and consequently be more vigorous. The appropriateness of 



