I 



I 



GROUP IV. — PHANEROGAMIA : GYMNOSPERMiE. 467 



parenchyma (Arancarinese, Taxoideae, some CupressineeB and Taxo- 

 dineae, the Cjcadaceee and Gnetacece). 



A remarkable feature in the histology of Welwitschia is the 

 presence in the ground-tissue of large thick-walled fibrous cells, 

 called spicular cells^ in the walls of which crystals of calcium 

 oxalate are deposited ; the occurrence of these crystals in the cell- 

 walls, is common throughout the class (Fig. 65). 



The General Morphology of the Reproductive Organs. The repro- 

 ductive organs are microsporangia (pollen-sacs) and macrosporangia 

 (ovules) : the microsporangia are always borne on sporophylls, but 

 the macrosporangia are sometimes borne directly on the axis 

 {e.g. macrosporangia of Taxeee and of the Grnetaceae) : they are 

 developed on distinct shoots, and frequently on distinct plants 

 {e.g. Cycadaceae: some Coniferse, such as most AraucarinesB and 

 Taxese; Gnetaceae generally). 



Certain shoots are more or less clearly differentiated b,8 flowers; 

 the only exception being Cycas in which there is no proper macro- 

 sporangiate flower. The flower is always monosporangiate : its 

 sti'ucture varies widely ; it may consist merely of a terminal 

 sporangium invested by a few small bracts {e.g. macrosporangiate 

 flower of Taxeae) ; of a terminal sporangium with a rudimentary 

 perianth (macrosporangiate flower of Gnetacae) ; of one or more 

 sporophylls borne on a short axis and surrounded by a perianth 

 (microsporangiate flower of Gnetaceae) ; or of a larger or smaller 

 number of sporophylls arranged on an elongated axis, the whole 

 forming a cone. 



In the Gnetaceae the flowers are arranged in spicate inflor- 

 escences, and are situated in the axils of bracts which are more 

 highly developed in this order than in any other Gymnosperms. 



The Sporophylls are of two kinds, distinguished by the nature 

 of the sporangia which they respectively bear, as microsporophylls 

 and macrosporophylls. When the flower is a cone, the sporophylls 

 have a general resemblance to scaly leaves : in other flowers 

 (Taxeae, Cycas, Gnetaceae) they have various and specialised 

 forms. 



The microsporophyll (stamen) ocenrs in its simplest form in the 

 Cycadaceae, where it is a large stout scale bearing usually an in- 

 definite number of microsporangia on its under surface. In some 

 of the Coniferae {e.g. Pinus), the microsporophyll essentially re- 

 sembles that of the Cycadaceae, though it is much smaller (in 

 proportion with the smaller flowers) and bears only two micro- 



