The origin and formation of the pollen wall and Ubisch bodies of wheat (Triticum aestivum) have been investigate d. Two layers of callose surround the developing sporocyst: the first layer formed [MATTER UNCLEAR IN PDF FILE]e ual in distribution and is believed to push the sporocyst against the tapetum, while [MATTER UNCLEAR IN PDF FILE]second layer completely surrounds each cell and is believed to act as a temporary wall [MATTER UNCLEAR IN PDF FILE] cell develops. The pollen wall is initiated in conjunction with the plasma membrane. The plasma membrane protrudes toward the microspore coat and at the end of each protrusion there is a small patch of electron dense material that is the beginning of the probacules. The probacules continue to enlarge and the protectal fibrillar-reticulate pattern becomes evident. A trilamellar structure forms on the surface of the plasma membrane. Material deposited on this structure appears to be the beginning of the foot layer. Eventually the foot layer increases in thickness and connects the bases of the probacules. The reticulate pattern of both the tectum and the foot layer becomes clearly visible. The deposition of sporopollenin appears to take place on the sides and to extend toward the center of each reticulate unit forming the microchannels. Strands are formed at the proximal surface of the foot layer. These strands accumulate little sporopollenin on their surface and they represent a rudimentary endexine inTriticum. As the vacuole develops in the pollen grain, the endexine becomes appressed to the foot layer and can no longer be seen. The Z-layer forms between the endexine and the plasma membrane. As development continues, the intine forms between the Z-layer and the plasma membrane. Pre-Ubisch bodies are formed within the tapetal cells and pass through the plasma membrane. These form the core of the Ubisch bodies and it is on these that sporopollenin is deposited. The formation of the Ubisch bodies closely follows the pattern described for the pollen wall.