THE AMERICAN BOTANIST. 
69 
plant food and the second year to flowering, but by planting 
the seeds of such plants in autumn, we may induce them to 
produce seeds before the next autumn or within a year. Con- 
trasted with the behavior of these seeds is that of a few others, 
which not only do not germinate the year following the one in 
which they were produced, but remain dormant for many 
years — possibly twenty years or more. The cause for this 
delay in germination is not very plain and Mr. William 
Crocker of the University of Chicago has been investigating 
the subject. In the Botanical Gazette for October, some of his 
conclusions are published. In general he finds that a delay 
in germination is due to the seed coats which so completely 
shut out moisture that the embryo cannot get enough of it for 
growth. This is true of the Indian mallow (Abutilon avicen- 
nae), only a small per cent of whose seeds will grow after 
weeks of soaking. If the seed coats are broken, however, 
practically every seed will grow in a very short time. Es- 
sentially the same conditions govern the germination of our 
common plantains {Plant ago major and P. Rugelii) 
the shepherd's purse {Capsella bursa-pastoris) the pig- 
weed (Chenopodiiim album) and the cypress spurge 
(Euphorbia cyparissias) . A few other seeds will ab- 
sorb water readily, but the seed coats are so impermeable to 
oxygen, another essential, that until the seed coats are injured 
the embryo cannot grow. In the fruit of the clot-bur (Xanthi- 
nrn Canadense) there are two seeds of different shapes, one 
above the other. The lower one of the two usually grows 
the first year, but the upper seed, remains dormant for long 
periods of time, waiting for the necessary oxygen. Axyris 
Amaranthoides is another plant which produces two seeds of 
different shapes, but these are on different parts of the plant, 
instead of in the same bur. Owing to a difference in the 
thickness of the seed coats, one shape of seed will germinate 
at once, while the other remains dormant for years. Among 
our common hawthorns {Crataegus) the delay in germination 
appears to be due to some peculiarity of the embryo, which 
is not understood at present. It is a question whether the 
delayed germination of seeds has been evolved by plants to 
give the seeds a distribution in time, or whether it is an in- 
herited tendency of no special value to the species. 
