An Historical Sketch . 8r 
integuments increase in size and become fused with and an integral part 
of the carpel. 
Celakovsky does not suppose, as was thought by Strasburger, that the 
various transitional forms represent the different stages of development 
which are to be run through in order to reach the extreme form ; nor does 
he regard it as ever possible that the integuments could, once they are 
laid low, revert back into a carpellary segment. A series composed of 
metamorphosed structures is of greater morphological importance than 
a developmental series. 
Strasburger asserts that each of these forms ought to be treated and 
studied separately, in and for itself alone. Our author, on the contrary, 
affirms that £ each single case taken by itself is of little value ; it is only the 
comparatively arranged complete series which can guarantee us real insight 
into the essential being, metamorphosis, and origin of the ovule.’ 
Our author further urges that a comparison of an orthotropous ovule 
with the macrosporangium and sporocarp of Azolla tends to destroy 
Strasburger’s views founded on the ontogeny ; for the integument of Azolla 
arises not from the sporangium, but from the leaf-segment beneath it. 
And, moreover, as the present writer would add, Warming has clearly 
shown that both nucellus and integuments develop independently from the 
ovular rudiment. The terminal position of the nucellus does not prevent it 
from being altogether distinct from the ovular rudiment producing it. 
As regards the view held, for instance, by Balfour, that the nucellus is 
an organ sui generis , Celakovsky points out that inasmuch as, in the 
virescent ovule, the nucellus, as an emergence from the surface of the 
ovular leaflet, may become completely absorbed into, and form an integral 
part of, the latter, it cannot possibly constitute one of the distinct morpho- 
logical categories ; for the respective organs belonging to these latter have 
never been known to merge or be absorbed into each other in such a 
manner. The same will be true of the eusporangium of Vascular Crypto- 
gams, which is the homologue of the nucellus. 
General Summary. 
In conclusion is appended a brief resume of the various theories on the 
morphology of the ovule. 
Axial Theory. 
St. Hilaire (1830, 1840), Schleiden (1839, 1843), Payer (1859), Braun 
(i860), Peyritsch 1 (1872-76): the nucellus is of the nature of a bud bearing 
the two integuments as lateral foliar appendages. 
1 It must be borne in mind that this author nowhere makes any definite statement as to the 
morphology of the ovule, but his writings betray the trend of his ideas on the subject. 
G 
