of lower forms of Vegetation. 193 



either by the spongioles of the roots, or through the stomates 

 of the leaves. As far as our knowledge of the physiology of 

 the spongioles extends, it seems improbable that they have the 

 power of absorbing solids (for earths, etc., as silica, are ab- 

 sorbed in a state of solution), even when as minute as spo- 

 ridia ; nor does our imperfect acquaintance with the course of 

 the sap enable us to say, that along with it innumerable 

 spores can pass the long journey from the roots of an oak or 

 pine tree to the leaves ; this would be altogether an unproved 

 assumption. 



Besides, if these sporidia passed through the vascular 

 tissue of plants, of late years these structures have been ex- 

 amined with such scrupulous and scrutinizing care through 

 the most powerful microscopes, I should have conceived a 

 stray spore must have been observed before this time, and 

 yet none have ever been seen, simply, I presume, because there 

 are none there to see. But they may be absorbed through 

 the stomates into the leaves, and carried down along with 

 the woody fibres, which, according to the theory of Du Petit 

 Thouars, the leaves annually form. It is first necessary to 

 prove the openings of the stomates are large enough to allow 

 the sporidia to pass through them. If a sporidium of TJredo 

 or Puccinia is a single plant reduced to the most simple con- 

 dition, and not admitting of further subdivision, it is too 

 large to find access to the external structure of the leaf 

 through the orifices of the stomates ; but it may be said the 

 grumous contents of the sporidia of Puccinia and Uredines are 

 prolific, and can pass through the stomata. In our present 

 state of ignorance on this obscure subject, we can neither 

 prove nor disprove this point, and I would wish to state every 

 argument as fairly as I am able. Evergreens, which have 

 thick coriaceous leaves and a horny cuticle, are well known 

 to be very scantily supplied with stomates, and yet such 

 leaves are prolific of entophytous Fungi, e. g. the leaves of 

 Lauro cerasus, holly and ivy; this is a negative argument 

 against the introduction of spores through the exhalent 

 orifices. 



It is easy to produce some erumpent Fungi ; you have only 

 to break a living twig of oak so as to cause it to wither and 

 die, leaving it attached to the tree, and Cenangium quercinum 

 will appear beneath the bark. Now if this Fungus arises 

 from spores already contained in the tree, and only waiting 

 for the death of the twig to assume an active state of vegeta- 

 tion, the whole of the branches of the tree must be impreg- 

 nated with countless multitudes of the spores oi Cenangium 

 (not to say of many other Fungi), which is an assumption 



4nn.^ Mag. ISI, Hist, Vol.\\\. O 



