1906] CROCKER—DELAYED GERMINATION . 271 
point within their temperature limits, and the two seeds have almost 
identical temperature limits. Table III shows the relative speed of 
TABLE III. 
X. canadense; COATS REMOVED; TEMP. 18-22°. 
PER CENT. GERMINATED AFTER 
SEEDS 
3 days | 4 days 6 days | 9 days 
Uppers ce 47 75 84 100 
EOWEt ces: 51 vies 89 pice 
germination of the upper and lower seeds of X. canadense at 18-22°. 
The minimum germinative temperature for the upper and lower 
seeds of this species with the seed coats removed is about 18°. The 
same point for other species mentioned is 2~3° higher. Each seed 
of Xanthium has then two minimum germinative temperatures: one 
with the seed coat intact, and a lower one with the seed coat removed. 
In the upper seeds these two temperatures differ by fifteen or more 
degrees and in the lower ones by two or more degrees. Table IV 
gives the approximate germinative minimum temperatures for each 
TABLE IV. 
MINIMUM GERMINATIVE TEMPERATURES. 
i ini . °C. coats | Minimum temp. °C, 
a Seeds re Besson coats removed 
X. canadense......... 2. be fluctuating 25-41 
ower 2I 
X. echinatum.. . upper 32-33 19-20 
A ae lower 23 19-20 
me Pabratum: 205 sc tte fluctuating 25-41 - 
ower 
X. speciosum Sia sae byt sie fluctuating 25-41 oe 
ower 22 
of the four species with seed coats intact and seed coats removed. 
It is evident from the results so far given that ARTHUR’S statement 
that the difference between the two seeds does not lie external to the 
embryo, but in the embryos themselves, is entirely wrong. He over- 
looked the real point of difference, the seed coats, because of their 
aS delicacy and because of the ease with which they admit 
ater, 
