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 agreenhouse 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 3P;. If this plant is 
selected for further testing with self-pollinated seed, its progeny in the 
next generation will be labeled 3F, Ps P:, 3F1P;P2 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. 
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