60 SUMMARY OF CUREENT RESEARCHES RELATING TO 



Physiology. 

 Nutrition and Growth- 



Occurrence of Phagocytosis in the Root-nodules of Cycads.' 

 Franz Zack publishes his investigation of the nodules which occur on 

 the so-called " breathing-roots " of Cycads (compare the same author's 

 previous study of Elaeagnus), in their association with peculiar brown 

 excretion bodies. It is well known that special layers of the cortex in 

 Cycas are organized for the accommodation of the blue-green alga 

 Anabsena. These layers form a completely closed cylinder, interrupted 

 only at the growing-point. Within this zone an endophytic fungus 

 may be observed in the cells of the nodules, with its hyphae (5//. in 

 thickness) regularly distributed in the protoplasm. The hyphae in some 

 cells branch profusely, and these become coiled together. The fungus- 

 coils so formed are absorbed by an excretion-product ; the details of 

 this digestion-process are described. As the coils are organized, the 

 cell-protoplasm becomes divided, in a manner analogous to phagocytosis 

 in animals. During the digestion-process the nucleus shows signs of 

 degeneration, assuming at the same time a long spindle shape ; in a few 

 cases it was observed to divide by simple fragmentation. After some 

 time, often as soon as the coil is formed, protoplasm and nucleus are 

 disorganized. The author is of opinion that nodule-formation is not 

 due to the fungus ; nor is this a case of symbiosis, but of parasitism. 

 The fungus, it seems, infects tissues which are abnormally developed at 

 the expense of metabolism products ; and the cell reacts upon the fungus 

 by a process of phagocytosis. 



Effect of Injury to the Cotyledons upon Seedling development.! 

 Helene Jacobi concludes from experiments with seedlings of Phaseolus 

 multiflorus, Cucurbita Pepo, and certain Conifers, that this effect 

 is produced by the consequent disturbance of the food-reserves. 

 Diminution in the cotyledonary food-stores during the earliest periods 

 of vegetative development evokes acceleration in growth ; but the effect 

 upon the individual organs varies according to the species on the one 

 hand and the environment on the other. The experiments were con- 

 ducted in light as well as in darkness, and both water- and pot-cultures 

 were employed. In Phaseolus multijiorus, the bulk of the food-reserve 

 is stored in the cotyledons ; in this case their injury resulted in relative 

 lengthening of the stem, both in light and in darkness. In Cucurbita 

 Pepo and Conifers the seed-leaves are not so rich in food-reserves ; and 

 in this case the cotyledons displayed activity in growth when cultivated 

 in daylight, the increase in the stem being relatively feeble. The 

 Conifer seedlings grown in the dark, however, had abnormally developed 

 stems. The author concludes that while the seedling is dependent upon 

 its food reserves, it devotes its energies to stem development ; growth- 

 increase in the cotyledons occurs only in light of a particular intensity. 

 Emphasis is laid on the fact that the accelerated growth of the cotyledons 

 is due to the decrease in food-reserve, and not to the stimulus of 

 wounding ; and this is borne out by the case of an abnormal pine- 



* Oesteir. Bot. Zeitschr. lx. (1910) No. 2, pp. 49-55. See also Bot. Zeit.. lxviii. 

 (1910) p. 148. f Flora, n.s. i. (1910) pp. 279-289. 



