148 • Impacts of Applied Genetics— Micro-Organisms, Plants, and Animals 
beets, brussels sprout, cauliflower, tomatoes, 
citrus fruits, and bananas. Various horticultural 
plants— such as chrysanthemums, carnations, 
African violets, foliage plants, and ferns— are 
also being produced by in vitro techniques. 
Accelerating propagation and selection in 
culture is especially compelling for economical- 
ly important forest species for which traditional 
breeding approaches take a century or more. 
Trees that reach maturity within 5 years re- 
quire approximately 50 years to achieve a useful 
homozygous strain for further breeding. Spe- 
cies such as the sequoia, which do not flower 
until they are 15 to 20 years old, require be- 
tween 1 and 2 centuries before traits are sta- 
bilized and preliminary field trials are eval- 
A plantlet of loblolly pine grown in Weyerhaeuser Co.’s 
tissue culture laboratory. The next step in this procedure 
is to transfer the plantlet from its sterile and humid 
environment to the soil 
uated. Thus, tissue culture production of trees 
has become an area of considerable interest. 
Already, 2,500 tissue-cultured redwoods ha\e 
been grown under field conditions for compari- 
son with regular, sexually produced seedlings. 
(See app. II-B.) Loblolly pine and Douglas fir are 
also being cultured; the numher of trees that 
can be grown from cells in 100 liters (1) of media 
in 3 months are enough to reforest roughly 
120,000 acres of land at a 12 x 12 ft spacing.'* To 
date, 3,000 tissue-cultured Douglas firs ha\ e ac- 
tually been planted in natural soil conditions. 
(See figure 29.) 
'^D. J. Durzan, "Progress and Promise in I'oresl Cetielirs." in 
Proceedings, 50th Anniversary Symposium Paper. Srirnrr :ind 
Technology . . . The Cutting Edge (.\()pleton. U is: Institute of Paper 
Chemistry, 1980). 
Photo i*. . . • f 
A young Douglas fir free propagated 4 vcU!- 'Qo 'i,.*- , 
small piece of seedling leaf tissue. Three y« I' a-;-!' ■ 
at the test-tube stage seen in the loblolly pme : 'i 
