38 
CONTRIBUTIONS TO BOTANY. 
feature is not a constant character. Richard represents the 
ovaria as being immersed within a fleshy receptacle ; this, how- 
ever, is an erroneous view of the case : the receptacle is, in fact, 
merely a cylindrical axile column, upon which the ovaria are 
imposed, thus resembling an abbreviated spikelet, round which 
the flowers are densely crowded ; from this receptacle a secretion 
exudes, which flows between the ovaria, and finally agglutinates 
them and all the lower portion of the spikelet into one compact 
mass. Sometimes, however, this agglutination is only partial, 
especially towards the middle and summit of the inflorescence ; 
and it then occurs that many of the achsenia, perfectly mature, 
are as free as in Calycera, which fact I have frequently observed 
in Acicarpa tribuloides : even in the typical species the ovaria of 
the upper florets always remain free, as Richard has described 
them* ; but in that species these free achsenia seldom perfect 
their seeds. In Acicarpa the calyx, which is adnate to the ova- 
rium, is deeply 5-sulcate, the prominent midrib of its five free 
teeth being continuous with its salient angles ; at first it is of 
delicately thin texture, and extremely transparent, consisting 
apparently of two integuments with a fluid or vacant mesodermal 
space between them ; for the one can be made to move loosely over 
the other by pressure. The subsequent increment of the calyx 
seems to arise from the deposition of solid matter (probably de- 
rived from the receptacle) within the mesodermal space : the 
midribs of the calycine leaves seem to acquire the greatest 
amount of increment, becoming lengthened into thick pungent 
spines ; the calycine lobes are at the same time expanded into 
the globose nodules that form the bases of the spines ; while the 
external surface of the calycine tube becomes horny and solid^ 
the mesodermal space, being much enlarged, is filled with com- 
pact cellular tissue, which dries into a light spongy or pithy 
substance. While this deposition is taking place within the in- 
teguments of the achsenia, a similar exudation from the recep- 
tacle flows between the numerous achsenia, and agglutinates 
them, together with the receptacle, into one solid echinate glo- 
bose head, as before described. This appears to be the nature 
of the change in the development of the fruit in Acicarpa. 
There is an evident difference in the growth that takes place 
in the calyx of Acicarpa and in that of Calycera : in the former 
the excrescent spines are shorter, nodose at their base, subulate, 
with a small groove along their inner face ; in the development 
of the spines in Calycera the calycine lobes disappear or become 
entirely expanded into divaricated spines of much greater length 
and thickness, subulate and semiterete in form, being flattened 
Mem. Mus. vi. 46, tab. 11 b. fig. 5. achaenia coalita, fig. 6. alia libera. 
