124 peesidbnt's address. 



sub-tropical pollen is mostly sticky, as in the Euphorbias, 

 Tobaccos, and Poinsettias. That of Hedychium coronariuni 

 exudes from the anthers in glutinous streams, and the pollen 

 grains of Cypripedium insigne and Rhyncospermiim jasminoides 

 lie embedded in a glutinous matrix. 



The formation of the daughter-cell walls takes place simul- 

 taneously over the whole surface, so the daughter-cells lie, with 

 their own walls, quite free, within the wall of the mother-cell. 

 The pollen of Dielytra spectabilis affords good examples of such 

 mother- and daughter-cells. The mother-cells of Monocotyledons 

 divide after a different fashion from those of Dicotyledons. In 

 the former a mother-cell divides into two, and each half again 

 into two, in the same plane, giving a discoid form ; whilst in 

 Dicotyledons and the higher Cryptogams the division takes place 

 in two planes at right angles to each other, yielding therefore a 

 cubic or tetrahedral form. 



Condition of Pollen. A pollen grain must contain proto- 

 plasm, which may be naked, as in the Algse and Crypotgams, 

 but which is usually enclosed by a double wall of cellulose, the 

 Intine and Extine, as in the Phanerogams. The inner wall, or 

 Intine, is generally a complete cellulose sac, smooth and clearly 

 defined outwardly, though it may have inner thickenings which 

 merge imperceptibly into the pi'otoplasm. This Intine retains 

 the power of growth, and of its own cellulose can build up pollen 

 tubes. Sometimes the Intine thickens and protrudes through 

 the Extine at certain spots, as in Cuphea platy centra, whilst in 

 others there is an Extine lid as in Passiflora ccerulea. The 

 number of these spots is always definite, not only in species but 

 even in genera and families. Sachs says, "In most Monoco- 

 tyledons and in a few Dicotyledons there is only one ; in Ficus, 

 two ; in Onagracea, Cupuliferce, Geraniacem, Composite, and 

 Boraginece, three ; in Impatiens, Astrapcea, Almcs, and Car- 

 pinus, four to six ; in Convolvulace<B, Jlcclvacece, Alsinece, etc., 

 numerous." 



The outer wall, or Extine, may be an entire sac or a mere 

 enclosing network of cellulose which has passed into cork, with 

 meshes small or large, and threads fine or coarse, regular or 



