SPERMATOPHYTES 
lamina had disappeared and only the prominent ribs persisted. In 
some cases, however, the seeds replace sori on ordinary fernlike leaves 
(fig. 422). There are very many detached paleozoic seeds which have 
never been connected with the plants that produced them; but doubt- 
less many of them belonged to the Cycadofilicales. So far as these 
attached and detached seeds 
have been sectioned, they show 
certain features in common 
which are regarded as primi- 
tive. In seed plants the mega- 
"1* 
FIG. 421. Seeds of Aneimites (an American 
form). After WHITE. 
sporangium has long been 
called an ovule. In general 
structure it consists of a central 
region (the real sporangium) 
called the nucellus, which is invested by one or two coats called integu- 
ments. A passageway (micropyle) is left through the integument at 
the tip of the nucellus. When the changes occur that transform the 
ovule into the seed, the integument develops in various ways to form 
the seed coat or testa. In fossil seeds it is evident that the structure 
of the ovule must be inferred from the structure of the seed. 
In the seeds of Cycadofilicales 
there is a three-layered testa, which 
is often peculiarly free from the 
nucellus. The vascular strand that 
enters the seed divides into two sets 
of branches, one set traversing the 
testa, and the other traversing the 
outer region of the nucellus, in case 
the testa and nucellus are free. The 
nucellus is beaked, and contains a 
deep chamber (pollen chamber), 
which serves as a gathering place 
for microspores, and which in living gymnosperms is associated with 
swimming sperms. A remarkable feature of the seed, and of all paleozoic 
seeds that have been sectioned, is that there is no trace of an embryo. 
Since the embryo is present in mesozoic seeds, its absence from paleozoic 
seeds must be due to other causes than failure to be preserved. 
Stamens. The microsporangiate structures (stamens), first recog- 
nized in 1905, have been found to be of at least three types. They are 
FIG. 4*2- -Seeds of Pecopterh on 
ordinary fernlike leaves. After GRAND' 
