THE DISK.— STYLOPODIUM. 265 
‘transverse inflexions of the tubular cell-wall of the pollen- 
tube exist every now and then ;’ so that then ‘the pollen-tube 
is really a tube formed by elongated cells’ ; and hence having 
as many cavities as cells. In Dicotyledons, however, the pollen- 
tube appears to be in all cases unicellular, and, therefore, to have 
one continuous cavity. 
2. THE DISK. 
The term disk is variously understood by botanists : thus, 
by some it is used as synonymous with thalamus, receptacle, or 
torus (see page 292) ; by others, it is understood to include all 
abnormal or irregular bodies of whatever form or character which 
are situated on the thalamus between the androecium and gynce- 
cium ; by others, again, it is defined as that part of the thalamus 
which is situated between the calyx and the gyncecium, and 
which forms a support to the corolla and andrcecium ; while 
others, again, define the disk as the portion of the thalamus 
situated between the calyx and gynecium, when that part 
assumes an enlarged or irregular appearance ; and lastly, the 
term disk is understood to include all bodies of whatever form 
which are situated on the thalamus between the calyx and 
gyncecium, or upon or in connexion with either of these organs, 
but which cannot be properly referred to them. It is applied 
in the latter sense in this volume. 
Although the disk is not an essential organ of the flower, it 
is best treated of in this place, as it is most commonly placed 
between the andrcecium and gyncecium, and therefore comes next 
in order as we proceed with our examination of the parts of the 
flower. The disk seems, in many cases at least, to be merely a 
modification of the andrcecium ; this appears to be proved not 
only from its parts occasionally alternating with the stamens, as 
in Gesnera, but also from the circumstance of portions of it when 
highly developed becoming occasionally changed into them. It 
is frequently of a nectariferous nature, and hence was treated of 
by Linnzeus and many succeeding botanists under the head of 
Nectaries. We have already referred to nectaries under Glands 
(page 71) and Corolla (page 240). 
The disk is developed in a variety of forms; thus, in the 
Orange and Rue (jig. 579), it forms a fleshy ring surrounding 
the base of the pistil; in the Tree Peony (fig. 580), it occurs 
as a dark red cup-shaped expansion covering nearly the whole 
of the pistil except the stigmas ; in the Rose and Cherry (jig. 
544), it forms a sort of waxy lining to the tube of the calyx ; 
and in Umbelliferous plants the disk constitutes a swelling on 
the top of the ovaries adhering to the styles (jig. 578, d) ; this 
latter form of disk has been termed the stylopodivm. In other 
cases the disk is reduced to little separate glandular bodies, as 
in Cruciferous plants (jig. 26, gl) ; or to scales, as in the Stone- 
