140 MEMOIRS OF THE NEW YORK BOTANICAL GARDEN 



the outer curved surface as the base. These channels are separ- 

 ated from each other laterally (text-figure 2) by what are in 

 effect thick ridges on the inner surface of the contact wall of the 

 grain. Channels are thus formed which are roofed over against 

 the mass of the grain. There are approximately from 12 to 15 such 

 channels to each pollen grain. These so formed tubules are some- 



FiG. I. Longitudinal section through the apex Fig. 2. Cross-section of a pollen 

 of a pollen grain, showing the origin of the grain with its spherical base removed, 

 tubules. showing a diverging series of tubules. 



what flattened against the pollen grain, as shown by comparing 

 text-figures i and 2. They are more or less club-shaped, tapering 

 slightly toward the apex of the pollen grain and expanding and 

 separating from each other at their exposed ends. The tubules 

 have a much thinner coat than the walls of the pollen grain and 

 in many instances exceedingly delicate spinules can be observed 

 on their surface. The structure of a pollen grain of the Droser- 

 aceae may be compared to some extent to that of an Arcella. 

 The pore in the flat surface of the Protozoan serves as an out- 

 let for the pseudopods. In the case of the pollen grain the pro- 

 toplasm streams out through what seems to be a pore (text- 

 figure 2) formed by the inner walls of the tubules and enters the 

 mouths of the twelve to fifteen channels as shown in a median 

 section of a pollen grain in Fig. 41. 



The question as to the function of these tubules has not as yet 

 been fully determined by me. While Drude and Rosenberg believe 

 they are pollen tubes no adequate evidence has yet been offered. 

 It appears from observations of early stages that they are formed 

 at the time the walls of the pollen grain are thickened and lead 

 me to the belief that they are germ pores comparable to those 

 found in such families as the Ericaceae, (Enotheraceae, and others. 



