IN ORCHIDEi^ AND ASCLEPIADE/E. 529
SO to speak, of its mass, which in some cases produced its tubes lucrcl}^ on continued immersion in water. I even found that in this species, in the f:;radual decay of the n-^'j flower, where the parts remain soft, the rupture and pro- trusion of tubes took place while the mass w\as still in its original position, innnersed in the cell of its anthera/ The tubes produced in this situation often acquire a great length, but coming, immediately on their protrusion from the mass, in contact with the membrane of the anthera, their course is necessarily altered ; and in their new direc- tion, which is generally upwards, they not unfrequently arrive at the top of the cell, or even extend beyoiul it.
Tn addition to the several species of Asclepias already referred to, Cjinanchim {Viiicetoxicuiu) 7ii(jrum is the only plant of this family in which I have observed the whole of the appearances ; namely, the rupture of the mass, the production and protrusion of the pollen tubes, their union into a cord, with the course and entrance of this cord into the cavity of the style.
The present essay, therefore, as far as regards this family, might with greater propriety have been entitled, "On the mode of impregnation in the genus Asclepias." It seems, however, allowable to conclude, that in all the genera having pendulous pollen masses, the same economy, slightly modified perhaps in some cases, is likely to be found. But among those with erect pollen masses, there are several in which more considerable diftcrences may be expected. Of this section of the family I have hitherto had the opportunity of submitting only one plant to careful examination, namely, ITojjd carnosa ; and even here my observations are incomplete.
Tn Ilof/a carnosa I have never found the pollen tubes produced, or masses ruptured, while remaining in their original ])Osition ; but I have succeeded in producing these effects by bringing them in contact with certain parts of the corona.
The rupture and protrusion of ])ollcn tul)es, Ihen, take
' Tab. 35, fig. 11.
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