This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1907 Excerpt: ...of the stele, but would lie nearest to the dorsal surface on which the leaves are inserted, and hence the ventral portion of the xylem-ring would be broader than the dorsal, as is actually the case " in these types. Another objection which may be urged against the belief that the stelar types characteristic of the ...
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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1907 Excerpt: ...of the stele, but would lie nearest to the dorsal surface on which the leaves are inserted, and hence the ventral portion of the xylem-ring would be broader than the dorsal, as is actually the case " in these types. Another objection which may be urged against the belief that the stelar types characteristic of the Lindsayeae are immediately derived from those found among the Gleichenias, is the fact that while the latter belong to the lowest soral grade--the Simplices, the former are typical Mixtae. It is however perfectly possible to suppose that in some cases the evolution of a "mixed" type of sorus took place with comparative rapidity from a primitive condition, while the stelar system was relatively little modified, and this interpretation is strengthened by the fact that transitions from one type of sorus to another are known within the limits of a single genus in more than one instance. The evolutionary series indicated is also very strongly supported by evidence from the anatomy of the young plants of the more advanced Leptosporangiate ferns, a topic with which it will be more convenient to deal separately in a later lecture. Factors In The Evolution Of Solenostely. Having thus traced the evolution of the solenostele from the protostele through a very complete series of intermediate forms, it remains to enquire as to the factors which have brought about such a course of evolution. The first point we have to notice is that the solenostele is normally associated with the arched type of leaf-trace, i.e. with a type which itself resembles a solenostele incomplete on one side. It is a striking fact that this type of leaf-trace is also found in many protostelic forms. We saw in the second lecture that the C-shaped type of petiolar strand is ...
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