June 5. 1916 Histology of Strawberries 363 



pass the point of intersection and penetrate a short distance beyond 

 (PI. XUX, H). 



Brown/ working with thin disks of tissue cut from various plants, 

 particularly tubers of the potato and roots of the turnip, immersed in a 

 strong extract from the germ tubes of Botrytis cinerea, noted that the 

 separation of the cells followed the line of the cell walls, the cells on 

 either side being left intact. His idea of the destruction of the cells is 

 that the middle lamella is first dissolved, in consequence of which the 

 tissue readily falls apart along the line of the m^iddle lamella. Very soon 

 the remainder of the cell wall disintegrates and the whole structure 

 becomes very fragile.^ In no case was complete solution of the cell w^all 

 observed. Death of the cells ^ takes place at a late phase in the process 

 of disorganization of the cell walls. He observed also that in all cases 

 if a cell w^all was disintegrated death of the cell ensued; on the other 

 hand, if the cell wall was not affected neither were the living contents of 

 the cell.* 



Brown's conclusions satisfactorily explain the condition found by the 

 writer in strawberry cells attacked by Botrytis sp. Certainly the fungus 

 is able to penetrate the cells of the host while they are still fairly normal 

 in appearance and while the cytoplasm is still distinguishable (PI. XLIX, 

 B, D, G). The writer did not find, however, in any of the strawberries 

 examined cells which were unaffected by the action of the fungus. 



RESULTS OF INFECTION OF STRAWBERRIES BY RHIZOPUS SP. 



In contrast to the condition of strawberries rotted by Botrytis sp., 

 berries rotted by Rhizopus sp. show the following characteristics. The 

 berries soon become flattened, with considerable loss of juice. Micro- 

 scopic examination shows that the hyphae are characteristically close 

 to the surface of the berry, the majority being found in the outer six or 

 eight cell layers. Hyphae rarely or never penetrate the cells of the berry 

 under field conditions or when kept in moist chamber. The nuclei of 

 the cells persist in apparently normal condition until the cytoplasm of 

 the cell has almost entirely collapsed. 



The crowding of the fungus in the outer portion of the berry is very 

 noticeable. Indeed hyphae frequently grow for some distance imme- 

 diately beneath the epidermis. Plate XLIX, /, shows a portion of such 

 a hypha in a section cut nearly tangential to the surface of the berry. 

 The sm^all, thick-v^-alled cells (heavy, lines) on the right are epidermal 

 cells; the larger, thin-walled cells (light lines) on the left are storage cells. 

 The hypha, which could be traced across several sections, grows between 

 these two layers of cells for a considerable distance without penetrating 

 either. A similar condition is shown in vertical section in Plate XLIX, 



' Brown, William. Op. cit., p. 333. 'Ibid., p. 347. 



2 Ibid., p. 333. < Ibid., p. 345. 



