714 



SCIENCE 



[N. S. Vol. XLI. No. 1063 



second, the necessity of a flow for the trans- 

 port of substances inducing growth; and 

 third, the retention of these substances 

 (even beyond need) by or near the organs 

 which are first induced to grow or regen- 

 erate. 



Such a view is supported by the older 

 experiments of the writer on Tubularia. 

 Tubularia is a hydroid consisting of a hol- 

 low stem attached with stolons to a solid 

 substrate, usually piles or rocks, and bear- 

 ing at its free end a polyp. Only the re- 

 gion behind the hydrant and the tips of 

 the stolons show growth, the cells in the 

 stem do not grow any more. We can, how- 

 ever, induce the cells in any cross section 

 of the stem to grow into a polyp if we cut 

 off the rest of the stem above or beneath it. 

 How does this operation induce growth? 

 The first idea might be that this is due to 

 the wound; the wound, however, can only 

 be the indirect cause, since we perceive such 

 an outgrowth of polyps also from the tips 

 of the uninjured stolons. 



I observed that when we cut a piece ab 

 from the stem and if we suspend it in sea 

 water, both ends a and h form polyps, but 

 that the oral end forms its polyps consider- 

 ably more quiclcly than the aboral end ; and 

 the difference in time may be from one or 

 two weeks to one or two days, according 

 to the temperature and the species used for 

 the experiment. "We may, however, induce 

 the aboral end to form its polyps just as 

 quickly as it would form at the oral end if 

 we prevent the formation of the oral polyp 

 by cutting off the oxygen supply at this 

 end. Hence the suppression of the forma- 

 tion of the oral polyp accelerates the forma- 

 tion of the aboral polyp; and, conversely, 

 the formation of the oral polyp retards the 

 formation of the aboral polyp. This might 

 at first appear to be explainable on the as- 

 sumption that only a limited amount of 

 material for polyp formation was present 



in the stem, but this assumption is rendered 

 untenable by the fact that if we cut the 

 stem into a number of pieces each piece will 

 form two polyps, the oral one always more 

 quickly than the aboral one. This shows 

 that the stem has material enough not for 

 two, but, if necessary, for a dozen polyps or 

 more. "We understand the facts, however, 

 on the assumption that the material neces- 

 sary to induce the cells at the front edge 

 to grow into a polyp collects first at this 

 end and is held here ; and that only later it 

 can also gather at the opposite end. This 

 is almost the same assumption as that made 

 to explain the phenomena in Bryophyllum. 

 But in the case of Tubularia the visible 

 phenomena directly support our assump- 

 tion. I noticed that the formation of a 

 polyp is always preceded by a dense collec- 

 tion of certain pigmented cells from the 

 entoderm which are carried like the blood 

 corpuscles of higher animals in the fluid 

 which circulates through the stem. These 

 red or yellowish cells always collect first at 

 the oral end of a piece cut out from a stem 

 of a Tubularia, but if we withdraw the 

 oxygen from this end they collect at once 

 at the aboral end. I mentioned that the 

 tips of stolons may grow out into polyps 

 without a wound. Whenever this happens 

 the formation of a polyp is preceded by a 

 gathering of the red cells in this tip. The 

 question then arises : "Why do these red cells 

 gather first at the oral end of a cut piece of 

 the stem ? I am not in a position to give a 

 definite answer to this question. I suspect 

 that phenomena of agglutination may play 

 a role in this case. All I wanted to indicate 

 was the connection which exists between the 

 transport of special material and the locali- 

 zation and inducement to growth.® 



9 These older observations of the writer may 

 possibly assume a greater significance in view of 

 the work of Jas. B. Murphy concerning the role of 

 lymphocytes in the prevention of the growth of 



