764 H. E. Knowtton 
As the water content of corn pollen is high, it is probable that osmotic 
pressure plays an important part, both in the swelling of the grain and 
in its subsequent growth. This idea is strengthened by the fact that a 
definite concentration of sugar is necessary, any departure from which 
results in failure to germinate or in abnormal germination. It is difficult 
to understand why a definite concentration would be necessary if colloidal 
imbibition played the main rdle. On the other hand, the water content 
of Antirrhinum pollen is low and the pollen germinates in almost any 
concentration of sugar. Imbibition is probably more important here 
than is osmosis. 
Results were so variable that it was thought best not to use artificial 
germination as a test of viability in the experiments on longevity of corn 
pollen. Only fertilization tests were employed, therefore. 
Apple (Pyrus malus L.) pollen resembles Antirrhinum pollen in that 
it is easy to germinate and is not sensitive as to the concentration of eugay 
solution, as is indicated in table 5: 
TABLE 5. Germination or AppLte Potien (25° C.) 
Length 
Sugar solution Germination of pollen 
tubes * 
Per cent Per cent 
De ere nal crTeNt pips ana Satay CoH Sant htye MEN Nt Naat EASY uct gp a et Short 
Sel Oana hepa MA ects rag aay gy IM er yuh el ete RNS larg 8) Pearle ma 2 Short-long 
(he OMe gia ele Sean Meas en MEE eee aly Si ee keel ya ae WAR lige 8 Short-medium 
MOB Osetra etre tye Mem at At err aim ma nncgs Atar: CN ec terth tin Ney Ra 12 Short-medium 
IPAs (Oa Seana ag RE ILM AAPA ARNESON tad MLS ena Bel EN NR eat 15 Short-long 
TIAGO) ae SMO ye Ter a AP Pg) Me eng AR Dam uate 30 Short-long 
Lips Oey hei lan abd adele sae ere Han tn wk Ee eh WW Das e nl LOU ae 40 Short-long 
ZO ROVE eirarcy. emerinces Tair aba, Je) dae Sea ee eR ey Rl ee 20 Short-medium 
DD (Da rest ara aye hi aad RG OMG roan taaethd cr Nana ce Neg inn eee 7 Short 
PAY AO oe Be ek ve gee eee hee NA a AS CITA ae UA ARTE nereg Cibola. 30 Short-medium 
DOA ames eH Mee eer L Dia cin ntUsey Mee A Raa bt pe sae oy ne aa 30 Short-medium 
CAO) (0) Sti etapa Gea A grat ee PRL a CAP RR tea cK RE Da OR 25 Short-long 
* Short signifies a length of from 1 to 5 pollen-grain diameters; medium, a length of from 5 to 10 pollen 
grain diameters; and long, a length of from 10 to 25 pollen-grain diameters, 
Altho Knight (1918) found that the addition of pieces of the stigma 
to the medium exerted no favorable action, the author thus procured 
stimulation repeatedly, and even chemotropism. It was On as pronounced 
as with Antirrhinum pollen, however. 
