310 



SCIENCE. 



[N. S. Vol. XVIII. Xo. 453. 



is active in nourishing the prothallium is 

 probably correct; an interpretation I had ar- 

 rived at from a study of Taxodium." 



I discussed somewhat in detail the structure 

 and function of this tissue in a paper given 

 before the Society for Plant Morphology and 

 Physiology at its Washington meeting in 

 1903. In a brief summary of the paper* this 

 sentence occurs : " The spongy tissue is not 

 disintegrating tissue, as previously stated, but 

 it forms a zone of physiological tissue which 

 plays an important part in the nutrition and 

 support of the developing gametophyte." 



In a paper appearing in the current num- 

 ber of the Botanical Gazette (July, 1903), 

 Cokerf devotes three pages '•% a discussion 

 of this tissue in Taxodium, designating it 

 ' The large-celled tissue or tapetum.' His 

 very clear description is accompanied by sev- 

 eral figures representing this tissue at different 

 periods in the development of the gametophyte. 

 He finds that a definite band'^^ large-celled 

 tissue is early organized about the macrospore 

 separating it from the disorganizing nucellar 

 tissue. This large-celled layer continues un- 

 til the prothallium has nearly or quite reached 

 maturity. He ascribes to this tissue ' an active 

 part in the nourishment of the young gameto- 

 phyte,' and believes that it ' may be considered 

 as a tapetum.' But he makes no reference at 

 all to the application by Lang of the term 

 tapetum to a similar tissue in Stangeria; 

 neither does he in any way indicate that the 

 active nature of this tissue has been noted by 

 any other investigator. Furthermore, one 

 can but be surprised to find such unqualified 

 statements as : ' Moreover, this tissue in the 

 AbietesB is always spoken of as disorganizing ' ; 

 and, ' I do not know of any case, however, 

 where this tissue is said to persist in later 

 stages.' 



The tissue in contact with the outer sur- 

 face of the gametophyte during its period of 

 growth in Taxodium, as described and fig- 

 ured by Coker, is very similar to that occur- 



* Ferguson, ' The Development of the Pro- 

 thallium in Pinus' Science, N. S., 17; 458. 

 March, 1903. 



t Coker, ' On the Gametophytes and Embryo of 

 Taxodium.' Bot. Gae., 34. July, 1903. 



ring in Pinus. The various stages in the 

 life history of the spongy tissiie in Pinus are 

 fully described and illustrated in a paper now 

 in the process of publication, and I will not, 

 therefore, repeat the details of its develop- 

 ment here. 



The presence of an active tissue about the 

 growing prothallium in many gymnosperms is 

 now an established fact, but our knowledge of 

 the true nature of this tissue remains for the 

 present more or less obscure. Lang (1900) 

 speaks of it as both sporogenous and tapetal 

 in nature. Coker (1903) suggests that it 

 may ' represent an originally archesporial 

 tissue which has given up its function of 

 spore production and taken up the new role 

 of nourishing the young plant within,' but 

 he prefers to consider it a tapetum. It is not 

 impossible that these cells are sporogenous in 

 nature, each being a potential macrospore- 

 mother-cell, but in a careful study of their 

 origin and development I find no evidence 

 that such is the case. If they represent the 

 sporogenous tissue of some remote ancestor, 

 they have beyond any question now lost their 

 primitive function and have acquired a new 

 and important function in connection with 

 the development of the gametophyte. It is 

 probable that this tissue not only passes on to 

 the endosperm the nutritive substance derived 

 from the nucellus, but that it is itself active 

 in the manufacture of food, as Coker reports 

 the presence of numerous starch grains within 

 its cells in Taxodium and I have often ob- 

 served them in Pinus. Furthermore, I be- 

 lieve that, in addition to its physiological 

 role, this tissue serves an important mechan- 

 ical purpose. It not only affords support for 

 the prothallium during the long period in 

 which it consists of a thin layer of cytoplasm 

 containing free nuclei, but, gradually receding, 

 it pushes before it, as it were, the tissue of 

 the nucellus, thus making room for the growth 

 of the delicate gametophyte. 



There is certainly a very strong analogy 

 between this tissue and a tapetum, but we are 

 entirely in want of any evidence that the two 

 are homologous structures. It does not, 

 therefore, seem to me wise at present to ap- 

 ply to it the name tapetum, or to suggest a 



I 



