8 MISCELLANEOUS PUBLICATIONS 1251, U.S. DEPT. OF AGRICULTURE 



Table 2. — Light, temperature, and humidity requirements and development of selected, plants 1 — Continued 



Species : 



Conditions used in growth chambers 



Temperature 

 Illumination Photoperiod (day-night) Humidity 



Plant development under average 

 greenhouse conditions 



Height in- 



4 weeks 8 weeks 



Bloom Maturity 



Ft.-c. Hours 



Tobacco 1,200 14 



Tomato 1,400 14 



Turnip 1,200 12 



Wheat 1,600 16 



Wild buckwheat 1,200 12 



Wild mustard 1,400 12 



Wild oat 1,600 16 



° c. 



Percent 



Cm. 



30-25 



60 



1 



25-25 



50 



20 



25-20 



60 



10 



30-20 



40 



25 



25-20 



50 



30 



23-18 



55 



30 



30-20 



40 



25 



Cm. 



Days 



10 



120 



61 



50 



35 





61 



70 



.. 



50 



_. 



28 



70 



60 



Days 



140 

 100 

 65 

 100 

 65 

 60 

 90 



1 Plant development is similar for a given species whether raised under growth-chamber conditions listed or average green- 

 house conditions. 



2 See index for scientific names. 



3 Edible pods in 45 days. 



4 Harvested heads. 



GERMINATION OF SEED 



The plants described here are primarily crop 

 species and their seeds are easy to germinate. 

 However, problems do exist with seed germination 

 of certain plant species. An extensive text on 

 plant propagation (6) has been published and 

 should be very useful if problems are encountered. 

 The germination methods used in the Fargo 

 laboratory will be discussed here. Additional 

 comprehensive information on seed germination 

 has been published by Andersen (1) and Barton 

 (3). 



Method 1 



A small flat, 30 by 20 by 10 cm., is filled with 

 5 cm. of vermiculite. The seed is placed on top 

 of the vermiculite and covered with 1.3 cm. of 

 vermiculite for such seeds as alfalfa and 2.5 cm. 

 for pea seeds. Very small seeds such as those of 

 tobacco are mixed with sand to increase the volume 

 for better distribution. These seeds are not covered 

 after seeding. The vermiculite is wetted from the 

 bottom. An enamel tray is placed under the flat 

 to maintain the moisture level. The flat with 

 tray is placed in an incubator at the desired 

 temperature for the required length of time. 

 If the seedlings are kept in the flat for an ex- 



tended period of time, a dilute nutrient solution 

 can be used in place of water. Metal flats should 

 be of stainless steel, or if galvanized they should 

 be coated with an asphaltic material to prevent 

 toxic levels of zinc from leaching into the germi- 

 nating medium. 



This method is generally the easiest and most 

 successful for many types of seeds. The advantages 

 of using vermiculite for germinating seed are as 

 follows: (1) It has adequate moisture-holding 

 capacity and aeration. (2) It contains virtually 

 no nutrients or toxic materials. (3) Roots develop 

 well in it. (4) It is light weight and easy to handle. 

 Although peat may be mixed with verimiculite 

 for some purposes, its high absorptivity may in- 

 terfere with subsequent chemical treatments 

 applied to the roots. 



Method 2 



Two pieces of absorbent paper toweling ap- 

 proximately 20 by 30 cm. are wetted thoroughly 

 and laid on a sheet of waxed paper of the same 

 size. The upper paper is folded back 5 cm., seed 

 is placed on the second paper along the fold, 

 and the upper paper is folded back over the seeds 

 again. The absorbent papers are rolled loosely 



