GROUP IV. — PHANEROGAMIA. 433 



The macrosporophyll, or carpel, bears (usually) macrosporangia 

 (see p. 78). In the Angiosperms the carpel, either by itself or by 

 cohesion with others, forms a closed cavity, the ovary, which is 

 frequently prolonged at its apex into a longer or shorter process, 

 the style, bearing at its summit a glandular surface, the stigma : 

 sometimes the style is absent, so that the stigma is sessile on the 

 ovary; within the ovary the macrosporangia are developed. In 

 the Gymnosperms, the macrosporophylls (when present) do not 

 cohere, either individually or several together; so that in this 

 group there is no ovary, style, or stigma; they are thus distin- 

 guished from the Angiosperms, in which there is always an 

 ovary. 



The Sporangia are of two kinds; microsporangia or poUen^sacs, 

 and macrosporangia or ovules. The development of the sporangium 

 is, in both, eusporangiate (see p. 73). The sporangia are, as a 

 rule, borne on the sporophylls ; but in some few cases (e.g. micro- 

 sporangia of Naias, Casuarina ; macrosporangia of Taxus, Poly- 

 gonum, PrimulacesB, etc.) they are borne on the axis. 



The microsporangia, or pollen- sacs, may be developed either 

 singly or in a sorus of two or more ; they may be very numerous 

 on the sporophyll, as in the Cycadaceee. When borne on the 

 sporophylls, they are developed on the lower (dorsal) surface of 

 the microsporophyll in the lower forms {e.g. Cycadaceee, Coniferae); 

 whereas in the Angiosperms they are usually developed both on 

 the upper (ventral) and the lower surfaces. 



The microsporangia either project freely or are embedded in the 

 placental tissue of the member bearing them. The multicellular 

 hypodermal archesporium is either a row or a layer of cells. The 

 archesporial cells undergo, as a rule, division, giving rise to the 

 sporogenous cells together with a more or less extensive transitory 

 layer of investing cells, the tapetum, which is eventually dis- 

 organised. 



The microsporangium is, as a rule, unilocular; but in a few 

 Angiosperms some of the sporogenous cells are sterile and, instead 

 of giving rise to spores, constitute walls which render the micro- 

 sporangium multilocular. The septa are either transverse, so that 

 the loculi are in a vertical row (e.g. species of Mimosese ; also some 

 Onagraceoe, such as Circrea, Gaura, Clarkia) ; or both transverse 

 and longitudinal, as in Rhizophora and Viscum. 



The microsporangium eventually dehisces, generally by a longi- 

 tudinal slit, less commonly by a transverse slit or by a pore. 



