128 ANATOMT AND PHYSIOLOGY OF 



of wMch, by true growth depending on nutrition, often comes to 

 exceed the diameter of the pollen-grain a hundred times. 



Ohserv. The graaules of the fovilla have given rise to many false asser- 

 tions ; Ad. Brongaiart, hi particiilarj thought he had discovered that tliey 

 agreed in form and size in each species of plant, and had an independent 

 motion, whence he compared them with the spermatozoa of animals 

 {''Ann. d, /So. nat^ xii. 40., xv. 381). Eob. Brown also {'' A Brief Account 

 of MiGTOscopic Ohserv. on the Particles contained in the Pollen of Plants^' 

 1828), although he discovered at the very time the molecular motion of 

 the fovilla-granules, was of opinion that a change of form might be perceived 

 in the larger granules (which he called particles). Agamst these state- 

 ments I was compelled to declare most positively (" Ueher d. pollen^' 30), 

 I neither found a definite form and size of the granules in the pollen of 

 any given plant, nor could detect in them movement of any other charac- 

 ter than that of the molecular movement ; to similar results came Fritzsche 

 (" Ueh. d. pollen,'' 24), who shewed that these very grains which had been as- 

 serted by Brongniart and Brown to change their form, were nothing but 

 starch grains, while other seeming granules were drops of oils j the ma- 

 jority of the smaller granules may, however, as in all protoplasm, consist 

 of proteine compounds. These granules are invisible in many fresh pol- 

 lens, since the fluid in which they swim has the same refractive power as 

 the granules, whence such pollen-grains are as transparent as glass lenses; 

 when their fovilla is mixed with water the granules at once become 

 visible. 



The fovilla seems always to be at rest in the pollen-grain when 

 it comes from the anther, unless Zostera (Fritzsche L c. 5QJ forms 

 an exception. But when the pollen-grain has germinated upon 

 the stigma, the foYilla exhibits a circulation similar to that of the 

 protoplasm of Vallisneria and Chara, flowing downwards in a 

 t3road stream into the pollen-tube, and back upwards on the oppo- 

 site side. 



Ohserv, This phenomenon was first seen by Amici in Portulaca (" Ann. 

 d. Sc. nat.'' ii. 68), subsequently in other plants, especially in Gourds and 

 in Ilihiscus syriacus {'^ Ann. d. 8c. nat.'' xxi 329). Since it appears that 

 no other observer (except Schleiden, who saw the circulation in pollen- 

 tubes which had been developed in nectar) has been able to see tliis pheno- 

 menon, it may be permitted me to mention how the observation is to be 

 made. In Portulaca it is not difiicult, if a freshly-impregnated stigma is 

 exposed to bright sunshine for a few mmutes, the style then removed 

 from the flower with forceps, and the stigma upon which the pollen tubes 

 are veiy quickly formed, is observed dry, with a power of at least 200 

 diameters. In the Gourd (for as Amici told me himself, his observations 

 were made on this plant, which in Italian is ^ucca, and not on Yucca as it 

 is stated in all books) a layer must be sliced from a stigma powdered 

 with pollen an hour previously, and this slice pressed moderately between 

 two glass plates, to heighten its transparency. 



In the development of a filament from the internal coat of the pollen, 

 we meet with a new analogy between the pollen-grain and the spores of 

 Oryptogamous plants, since we have evidently before us a process of germi- 



