32 James Stewart Wiant 



Methods of taking and interpreting data 



The methods employed in taking; data on damping-off were varied some- 

 what from season to season, depending largely upon the stage of seedling 

 development at which the disease first appeared. Thus, in the spring and 

 early summer experiments of 1926, emergence in the beds of norway spruce 

 and red pine was practically complete before more than a trace of damping- 

 off had appeared. Counts of all seedlings in three rows in each plat were 

 made on such beds as soon as emergence had taken place. Counts were 

 again taken of the final stand in the same rows in early September. Obser- 

 vations made during the intervening time indicated that the differences 

 between the two sets of figures represented losses caused by the disease. 

 Damping-off appeared in beds of white pine soon after the first seedlings 

 had pushed through the soil, and continued during and after the emergence 

 period. Because of this, a single count of the final stand was made in 

 Sepetmber, on four rows in each plat. 



During the season of 1927, losses from damping-off were evident in the 

 beds of norway spruce and red pine from the very beginning of the emer- 

 gence period. This fact, combined with the loss of a number of seedlings 

 by bird injury, 7 made frequent counts necessary. All plats were therefore 

 inspected at short intervals to record and remove from four rows in each 

 plat all seedlings which were damped-off and the stubs of seedlings which 

 had been broken off by birds. As soon as emergence was over, the sur- 

 viving seedlings were counted, and this was followed by another count at 

 the end of the season. The difference between the two indicated the loss 

 from damping-off during this period. Where losses from disease were 

 slight throughout the season, it frequently happened that the number 

 damped-off was more than equaled by the number of late-emerging seed- 

 lings which always appear in conifer seedbeds even many weeks after the 

 vast majority of seedlings have emerged. These differences are indicated 

 as plus figures under the heading of percentage of damping-off, as in the 

 1926 experiments. In all cases they are small and are entirely without 

 significance. 



In the beds of white pine, damping-off likewise appeared during the 

 general emergence period. The more severe bird injury in these beds 

 made it desirable to count only the final stand at the close of the season. 

 It is pointed out later in this work that the results of these experiments on 

 white pine cannot be accorded the same significance as those with red 

 pine and norway spruce. 



As a result of the unequal distribution of the losses resulting from bird 

 injury, a sound interpretation of the data obtained from the norway- 

 spruce and red-pine experiments of 1927 necessarily involved the intro- 

 duction of a correcting factor. This was done in the following manner. 



7 When conifer seedlings first emerge from the seedbeds, the immature cotyledons still inclosed within 

 the seed coat are borne at the tip of the hypocotyl. The type of bird injury referred to was occasioned 

 by the action of sparrows and goldfinches in feeding on these tips. As a result, only the broken hypocotyl 

 remained. The danger from bird injury existed only until the cotyledons were mature and the seed 

 coats shed. 



