282 BOTANICAL GAZETTE [april 



species of Acacia, as did Crocker (unpublished work) with Scirpus. 

 The length of time required by this treatment varies from a few 

 minues to several hours, depending upon the resistance of the coats. 



Boiling water or warm water, used as a forcing agent, has proved 

 effective in a number of cases where hard-coatedness is the cause 

 of the delay. Bruyning (3), working with the seeds of JJlex 

 europaeus, found that a treatment of 1-5 seconds with boiling water 

 raised the percentage of germination from 13 for untreated seeds to 

 53 • 5~75 • 5 for treated seeds. Honing (13) obtained his best results 

 with Alhizzia seeds by soaking them in water at 60° C. for at least 

 3 hours, while with Mimosa 60-70° C. proved most effective, as 

 did 70-75° C. for Pithecolohium. Soaking seeds of Crotalaria in 

 warm water proved disadvantageous. Bolley (2) states that 

 improvement in germination was obtained by this method if the 

 exposure was not long enough to kill the embryo. 



NoBBE (21) mentions Alexander von Humboldt as the first 

 investigator to use chemicals as forcing agents. From the time of 

 Humboldt (1793) up to 1873, the date of publication of Nobbe's 

 book, many investigators used as forcing agents a great variety of 

 substances, both organic and inorganic. The range of substances 

 used is more interesting than the results obtained. Moreover, 

 quickly germinating seeds were used and in such cases the effect 

 of forcing agents is not so striking as where dormancy is involved. 

 Of the more recent workers in this field, Lehmann (16) was 

 the first to emphasize the importance of chemical substances in 

 connection with germination. He showed that the seeds of 

 Ranunculus sceleratus are forced into germination by Knop's 

 solution, by soil, by soil wet with weak solutions of hydrochloric 

 acid, potassium hydroxide, ferric chloride, and hydrogen peroxide. 

 Two years later Gassner (10) found Knop's solution effective on 

 unthreshed seeds of Chloris ciliata, and more recently (11) has 

 shown that for several other seeds various nitrogen compounds, 

 especially nitrites and nitrates, are effective forcing agents. Chloris 

 ciliata was found to have a membrane impermeable to potassium 

 nitrate and magnesium nitrate, and from this Gassner concludes 

 that the effect is upon the seed coat alone. Lehmann (17) and 

 Lehmann and Ottenwalder (18), working with seeds representing 



