RECENT WORK, ETC. 471 



Koch has recently shown (15, p. 452) that in some lilies the 

 growing point of the stem altogether perishes, at a time 

 when the stem is scarcely half-grown, so that the later 

 stages of development, so far as that particular stem is 

 concerned, are gone through in the absence of any embry- 

 onic tissue. If the same thing occurred in an entire plant, 

 as may perhaps be the case in some annuals or other 

 monocarpic plants, we should have a mode of development 

 in which the whole of the embryo becomes converted into 

 permanent tissue. In plants generally, however, the 

 reverse is the case. The embryo, as it exists in the seed, 

 does not directly give rise to the entire organism, but 

 embryonic development is continued in every separate 

 growing point. Hence, perhaps, it is that the study of 

 embryology, in the ordinary sense, has led to less 

 important results in the vegetable than in the animal king- 

 dom, though this fact is also due to the extreme meagre- 

 ness of our present knowledge of the embryology of plants. 

 The application of the term embryonic tissue to the 

 meristem of all growing points, which has become so general 

 of late years (cf. Sachs, 16, p. 503), is not without its 

 dangers. We must not suppose that the meristem of a 

 growing point, in a plant at an advanced stage of develop- 

 ment, is really identical with the meristem of the actual 

 embryo. Suppose, for example, to take a concrete instance 

 from our immediate subject, that we wished to determine 

 whether, in a particular case, the polystelic or the mono- 

 stelic condition of the stem was the more primitive. The 

 study of the growing points in an advanced specimen of the 

 plant would not help us. We should find that if the branch 

 were polystelic so would be -its growing point also ; from 

 the earliest differentiation of tissues at the apex, the full 

 number of steles would be present. This is the case even 

 in a genus like Gunnera, in which we have every reason 

 to believe that polystely is a recently acquired character. 

 Only by having recourse to the embryo itself, to the first- 

 formed parts of the stem, could we satisfy ourselves that 

 monostely precedes polystely in the course of development. 

 The same principle holds good throughout. A given 



