73 



pollen grains of Ruppia are here described. Then follows 

 the ellipsoid form of many Monocotyledons, which M.Fritzsche 

 has drawn with a fold, as in Lilium, Pancratium. Cohesions 

 of two, as in Lilium candidum, and of four, as in Phillydrum 

 lanuginosum and Anona tripetala, are enumerated. More rarely 

 two opposite folds occur, as in Tigridia Pavonia ; on the con- 

 trary, frequently symmetrical longitudinal folds, as in Plum- 

 bago capensis. Globular pollen forms are more rare. Stre- 

 litzia exhibits them with an homogeneous outer coat ; Canna 

 presents small spines, and regular warts appear in Jatropha 

 panduraefolia. In Sowerb&a juncea the groove goes quite 

 round the vesicle, and the outer coat is thus divided into two 

 halves. Allied to this is the interesting form of the pollen of 

 Thunbergia fragrans and several species of Berberis. In 

 Commelina coelestis a large tabular piece takes off, which lies 

 on the aperture as a lid, and several such lids occur in the 

 genus Passiflora, where again a number of varieties originate 

 by the division of the lid, which are all minutely described 

 and figured. That portion of the outer tunic where the aper- 

 tures are closed by distinct lids is termed the skeleton of the 

 tunic. In Scabiosa the lid appeared as if merely formed by 

 the granular lining of the outer tunic. 



B. Grains with apertures. These forms are again subdi- 

 vided into two sections, according to whether the apertures 

 consist in fissures of various lengths, or form circular holes. 

 Three fissures, as in Geissomeria longiflora, is the smallest 

 number observed. In many Cyperacea four to five unsym- 

 metrical fissures are found ; the form of Car ex prcecox is fi- 

 gured where the inner tunic presents peculiar thickenings. 



The position of the fissures on the tetrahedral forms of the 

 pollen of some species of Corydalis and Basella is very re- 

 markable. The pollen of Talinum patens exhibits twelve fis- 

 sures, and Polygonum amphibium many more, the outer tunic 

 forming twelve regular pentagonal fields, each of which is sur- 

 rounded by five regular fissures. 



The group of pollen grains with round apertures presents 

 a greater variety of forms ; one aperture in the Graminece, 

 two apertures in Banksice and Justicia Adhatoda. Three aper- 

 tures are most frequent and occur in many plants in connexion 

 with three longitudinal grooves, which in general hide the 



