No. 380.] REVIEWS OF RECENT LITERATURE. 609 
these immature forms have been propagated in greenhouses under 
various names, “ Pothos,” “ Marcgravia,” — very much as the early 
shoots of Thuja, with the needle-shaped leaves, were for so long 
supposed to belong to a special genus, Retinospora. 
The reversion to the primitive leaf-forms in the seedlings and 
sometimes in older shoots of various water-plants and xerophytes is 
discussed at length, and their bearing upon the questions of the 
origin and affinities of these plants is admirably set forth. 
The fourth division of the work deals with malformations of 
various kinds, discussing in a very suggestive way their cause and 
significance. Goebel believes that the explanation of Sachs, who 
assumes that specific chemical substances are developed which 
determine the character of the various organs, is the most plausible 
one yet brought forward. Goebel’s explanation of the reason why 
malformations, especially the transformation of one organ into 
another, are so much commoner in the flowers than in the other 
organs of the plant, e.g., the roots, is because the young organs 
of the flower are formed in rapid succession, and close together, so 
that the specific substances properly belonging to one organ are more 
likely to reach one of another kind, thus producing a more or less 
transitional form. To quote from our author: “If, for instance, 
molecules of such substances as induce anther-formation should stray 
even by the thousandth part of a millimeter from their path, or 
should be checked or hastened in their transportation to the growing 
point of the flower, there would thus result a more or less complete 
transformation of the petals or carpels into stamens.” 
Goebel also quotes from Sachs to show that the latter conceives 
these “bliitenbildende ” substances to have somewhat the character 
of ferments, an extremely small quantity having power to affect large 
masses of plastic substance. A similar character is attributed by 
Beyerinck to what he calls “ growth enzymes,” produced by gall- 
forming insects, which so affect the protoplasm of the host-plant as 
to give rise to the specific gall-form. 
While these theories are certainly interesting and ‘not improbable, 
they seem quite as difficult to prove as the phylogenetic hypotheses, 
which Goebel in another part of his work seems to think so hopeless. 
The last division of the book has to do with the influence of 
correlation and external stimuli upon the form of the vegetable 
organism, and presents many interesting details which cannot here 
be discussed at length. 
Every botanist who is interested in morphological problems must 
