1907] SMITH—TRUNK AND MICROSPORANGIUM OF CYCADS 199 
three times longer than those in the room (jigs. 48, 49). These cultures 
gave an opportunity to study the breaking of the exine and the extru- 
sion of the tube (fig. 50). In the unstained specimens the portion 
of the wall just touching the prothallial cell and passing down either 
side of it was more refractive than the rest. In stained material 
(figs. 48, 49) this had the appearance of a lighter wall just within the 
intine, and agrees with the “third wall” described by Miss FERGUSON 
(24) in Pinus. Tlie starch in the growing tube is very abundant, 
massing about the tube nucleus and the generative cell (jig. 49); in 
longer tubes there is also a large quantity near the tip. The tube 
nucleus slowly migrates toward the tip, keeping just behind it. In 
Zamia there is no sign of the second prothallial cell mentioned by 
WEBBER (20), though many hundred microspores were examined. 
Microspores of Encephalartos, which are very large, were especi- 
ally favorable for a study of the divisions to the three-celled stage 
(jigs. 51, 52), which are like those described for Zamia. Only one 
mitotic figure was seen, but it shows the size and shape of the chro- 
mosomes fairly well (fig. 52). 
Summary 
1. The stem of Zamia floridana is a sympodium, a vegetative 
point lying at the base of each strobilus. The staminate strobili 
develop one after thé other from the successive vegetative points, 
each strobilus with a small circle of leaves, and all enclosed within 
the larger scale leaves of the first strobilus. 
2. The youngest staminate strobili received June 1 showed the 
sporophylls arising in acropetal succession, by a periclinal division 
of a hypodermal cell, and later by the divisions of other hypodermal 
cells and layers beneath them. 
3. The microsporangia cover the abaxial face of the sporophylls 
in Ceratozamia mexicana, and are grouped upon each flank in Zamia. 
In Dioon, Encephalartos villosus, E. Caffer, and M acrozamia Miquelii 
there are intergrades, where the sporangia cover the sporophylls of 
the central part of the strobilus, but are in two groups upon the 
sporophylls of the tip and base. 
4. The microsporangia are grouped in sori (two to six sporangia 
in each sorus), which are raised on a cushion of tissue into which a 
vascular bundle passes. 
