38 MORPPIOLOGY OF SPERMATOPHYTES 



THE BOOT 



Some account of the anatomy of the root has been published 

 by Van Tieghem. 2 It seems that the vascular cylinder is origi- 

 nally a diarch, and a little later each strand divides, resulting 

 in the formation of a tetrarch cylinder. Later, new strands 

 come in, so that five or six alternating xylem and phloem bun- 

 dles appear. Presumably the meristem of the apex shows the 

 same peculiarities as described under Conifers. 



II. THE SPORE-PRODUCING MEMBERS 



THE MICROSPORANGIUM 



The stamens occur in loose catkinlike clusters from the axils 

 of the scale leaves developed at the summit of the short shoot 

 (Fig. 30, B). It is this elongated catkinlike cluster of micro- 

 sporophylls which has received the inappropriate name of the 

 " male flower." The sporophyll has a rather long stalk and 

 terminates in a more or less expanded knob, which may be re- 

 garded as representing the expanded sterile tip common among 

 the Cycads. Beneath the knob the pendent sporangia are borne, 

 usually two in number, but sometimes three, or even four. The 

 dehiscence is by a longitudinal slit (Fig. 30, (7). 



There are no published details of the development of the 

 sporangium, but there is no reason to suppose that it is different 

 in any important way from that described for the Cycads. The 

 mature sporangium wall consists of four to seven layers of cells, 

 with thickening bands on the outer layers. 



THE MEGASPORANGIUM 



The structures associated with the megasporangium have 

 given rise to much discussion. A long stalk arises from an axil 

 of the leaves borne at the summit of a short shoot, and near its 

 apex mostly two megasporangia are borne, only one of which 

 functions (Fig. 30, A, E). About the base of each sporangium 

 is a more or less conspicuous cup or " collar," much more prom- 

 inent in the younger stages of the sporangium, reaching its full 

 development very early. Seward and Gowan 15 have published 

 a resume, of the various views held in reference to the homolo- 

 gies of these structures. Briefly they are as follows: 



