422 GENETICS IN RELATION TO AGRICULTURE 



of success. Anyone with ordinary ingenuity will usually be able to 

 provide the necessary protection. The important thing is to realize 

 its need in time to prevent loss or contamination of cultures. If the 

 breeding garden is located in or near cities the English sparrow will 

 work havoc with developing seeds, especially of cereals. This menace 

 can be completely overcome only by enclosing the threatened cultures 

 with something that will keep out the birds and at the same time cut off 

 the minimum amount of light. We have found 1-inch mesh poultry 

 netting satisfactory (see Fig. 170). Many plants used in genetic 

 investigations can be handled most satisfactorily in the greenhouse. 

 Fig. 171 shows a greenhouse filled with pedigree cultures of a single species. 

 A systematic method of recording and preserving data is sine qua 

 non for the pedigree culture. It is absolutely unsafe to trust to memory 

 if any degree of accuracy is to be attained. For work on a small scale 

 a serial number (using Arabic numerals) for each culture is satisfactory. 

 This number then becomes the permanent designation of the given 

 culture, each plant in the row receiving a subscript number. Thus 

 plant No. 5 of culture No. 3 would be designated as 3Ps. If this plant is 

 selected for further testing with self-pollinated seed, its progeny in the 

 next generation will be labeled 3Fi P 5 PI, 3FiP 5 P^ and so on down the 

 row of plants. However, this method is rather cumbersome and for 

 work upon a large scale the "annual-note-book-page" method first 

 described by Shull is much- more satisfactory. In this system each 

 culture of a given year is numbered chronologically receiving the number 

 of the page in the note book for that year on which it happens to be 

 recorded. The label bears this number preceded by the distinctive 

 numerals of that year. Thus the particular culture recorded on page 

 1 of the 1918 note book will be labeled 181 or 18.1. The use of the 

 decimal point is a convenience especially if one is working at an in- 

 stitution where serial numbers are in use in another department. In 

 addition to the annual note book a set of permanent index cards should 

 be arranged each year, including of course only those actually grown in a 

 given year. By writing the current year number in one corner and the 

 corresponding number for the preceding year in the other corner one has 

 a convenient system for securing the complete pedigree of a given cul- 

 ture. To complete this method some designation is necessary for the 

 individual plants selected in any year. This may be a number in paren- 

 theses, a subscript, a letter, or, where plants are set at equal distances 

 from a given base line and each plant is thus numbered automatically, 

 the letter P with subscript is satisfactory. Whatever the individual 

 designation may be, it becomes the name of the particular plant for the 

 remainder of its existence but its progeny will receive a new number 

 when the seed is sown. 



