276 BOTANICAL GAZETTE [march 



and 0. pycnocarpa and their hybrids, both of which species were formerly- 

 included in O. biennis. Many valuable confirmatory details need not be 

 cited, but the following may be mentioned. The embryo sac is 4-nucleate, 

 lacking antipodals and one of the polar nuclei, and this condition was found 

 not only in Oenothera, but also in Ludwigia, Gaura, Godctia, and Circaea. The 

 author regards it as a diagnostic character of Onagraceae, and therefore would 

 exclude Trapa, with its normal 8-nucleate sac, from the family. This condi- 

 tion in Onagraceae he thinks may have been produced by mutation, but not 

 by adaptation. The pollen tube enters the synergid and the "mixed plasma" 

 flows out and spreads over the egg. The cytoplasm of the pollen grain was 

 found to contain an immense number of minute starch grains, which migrate 

 through the pollen tube, enter the synergid, and finally disappear. The male 

 nucleus is inclosed in a distinct plasma sheath until it reaches the egg. The 

 synergid and the upper two-thirds of the egg have a distinct cellulose membrane, 

 the lower part of the egg acquiring it after fertilization. Self -sterility of some 

 hybrids is said to be due to the feeble growth of the pollen tube. — J. M. C. 



Histology of phloem. — There has been a tendency in recent years to assume 

 that the doctrine of recapitulation is a law as valid and invariable as the laws of 

 physics and chemistry, and to use it as a reliable short cut in the study of the 

 evolution of plants. However, it is to be emphasized that a law is a statement 

 of fact, not a theory or working hjrpothesis. If the doctrine of recapitulation 

 and similar generalizations are to be accepted as true laws they must be capable 

 of statistical or experimental proof. MacDaniels's points out that, although 

 in a considerable number of woody dicotyls which he studied there is no funda- 

 mental difference between the type of sieve tube found in seedhngs and first 

 annual rings and that found in the mature condition, the remaining forms pos- 

 sess a presumably less primitive type of structure in the earlier than the later 

 stages of ontogeny. Furthermore, he shows that there is no close parallelism 

 in the speciahzation oT sieve tubes, vessels, and floral structures. It has been a 

 common morphological fallacy to assume that because the evolution of a 

 selected structure progresses apparently in a given direction the sums of all 

 structures (organisms) are moving in a similar direction. MacDaniels' 

 comprehensive and painstaking piece of work is a valuable contribution to our 

 knowledge of the histology of phloem. — I. W. Bailey. 



Enzyme secretion. — The influence of such inorganic salts as the nitrates, 

 chloride sulphates, and monobasic phosphates of sodium and potassium, and 

 the chlorides and sulphates of calcium and magnesium on the secretion of 

 diastase by PeniciUium camemheriii has been investigated by Robbins.'^ 



'5 MacDaniels, L. H., The histology of the phloem in certain woody angiosperms. 

 Am. Jour. Bot. 5:347-378. 1918. 



'^ RoBBiNS, W. J., Influence of certain salts and nutrient solutions on the secretion 

 of diastase by PeniciUium camembertii. Amer. Jour. Bot. 3:234-260. 1916. 



