GROUP IV. GYAINOSPERM-E. 423 



the Angiosperms. In Grnetum, however, there are no microsporo- 

 phylls. 



The macrosporophyll (carpel) appears in" a simple, yet typical, 

 form in Cycas (see Fig. 253), the one Gymnosperm which has no 

 distinct macrosporangiate flower. Here the carpels are essentially 

 similar to the foliage-leaves, though they are smaller, of a yellow 

 colour, and of a somewhat different form : they are, in fact, de- 

 veloped at the growing-point of the stem in the place of a whorl 

 of foliage-leaves. The few sessile macrosporangia are borne 

 laterally on the lower part of the sporophyll. 



In the other Cycadaceae, the macrosporophyll is a stout seal}- 

 leaf, thickened at its outer end, bearing usually two lateral ovules, 

 one on each side. 



In the Coniferse, the simplest form of macrosporophyll is a scalj* 

 leaf bearing a single macrosporangium on its upper surface : in 

 other forms the superior surface of the macrosporophyll is clearl}- 

 marked out, by outgrowths of various kinds, into an apical and a 

 basal half, the latter alone bearing the (1-7) macrosporangia (e.g. 

 Cupressinese) : in the Abietinese (Pinus, Larix, etc.) the sporangi- 

 ferous structure of the preceding families is developed from the 

 base of the carpel as a placenta! scaZe, which is much larger than 

 the carpel itself, and bears the two macrosporangia on its upper 

 surface. In the Taxese the macrosporophylls are rudimentary 

 (e.g. Phyllocladus, Cephalotaxus) or absent (e.g. Torreya, Taxus) ; 

 even when present they do not bear the macrosporangia. 

 In the Gnetacese there are no macrosporophylls. 

 The microsporangia (pollen-sacs) are borne, in nearly all cases, 

 on the lower (dorsal) surface of a sporophyll ; they may be numer- 

 ous (about 1,000) as in some Cycadaceae ; or few (2-15) in the 

 Coniferse and Gnetaceaef scattered (some Cycads), or more 

 commonly grouped into one or more sori, with more or less well- 

 developed placental tissue ; either imbedded in the tissue of the 

 sporophyll (e.g. Abietinese), or freely suspended (eg. Grinkgo) : in the 

 Cupressinese, the sporangia, when young, are covered by an out- 

 growth of the under surface of the sporophyll which is comparable 

 to the indusium of Ferns. In Grnetum, as there is no micro- 

 sporophyll, the two microsporangia are borne on the apex of the 

 floral axis. 



The structure of the microsporangium is simple : it is unilocu- 

 lar; it contains, at an early stage, a mass of spore-mother-cells 

 derived from the archesporium, surrounded by a layer of ta petal 



